Liquid-crystal electro-optical apparatus and method of manufacturing the same

ABSTRACT

A liquid crystal device comprising:
         a pair of substrates having an electrode arrangement thereon;   an orientation control means provided on at least one of said substrates; and   a ferroelectric or antiferroelectric liquid crystal layer interposed between said substrates, said liquid crystal layer being uniaxially oriented by virtue of said orientation control means,   wherein means for suppressing an orientation control effect of said orientation control means with respect to said liquid crystal layer is provided between said liquid crystal layer and said orientation control means.

This application is a Divisional application of Ser. No. 08/592,672,filed Jan. 26, 1996; which itself is a divisional of Ser. No.08/278,088, filed Jul. 20, 1994 (now U.S. Pat. No. 5,594,569).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid-crystal electro-optical deviceof a birifringence mode using a ferroelectric or antiferroelectricliquid-crystal material.

2. Description of the Related Art

Recently, attention is paid to liquid-crystal display devices (LCD).Among them, in particular, the liquid-crystal display devices of thetwisted nematic (hereinafter referred to as “TN”) type using nematicliquid crystal and the super twisted nematic (hereinafter referred to as“STN”) type have been widely known and practically used.

Also, the liquid-crystal display devices of the active matrix type usingthe nematic liquid-crystal material in which a switching element such asa thin-film transistor (TFT) is provided for each pixel have beenextensively developed as the device capable of performing high speed,high-contrast and multi-gradation display.

The fundamental structure of the liquid-crystal electro-optical deviceof the TN type and the STN type will be now described. An orientationfilm is coated on a substrate having an electrode, sintered and thensubjected to rubbing as an orienting process to form a first substrate.Likewise, an orientation film is coated on a substrate having anelectrode, sintered and subjected to rubbing to form a second substrate.The first and second substrates are provided so that the respectiveelectrodes are opposed to each other, and liquid crystal is held betweenthese substrates.

On contact surfaces between the respective substrates and aliquid-crystal layer, the liquid-crystal is aligned in a rubbingdirection in accordance with a regulating force of rubbing. The rubbingdirections of the upper and lower substrates are shifted from each otherby 90° in the case of the TN-type device and by 200 to 290° in the caseof the STN-type device. The liquid-crystal molecules in the vicinity ofthe middle of the liquid-crystal layer are aligned in the spiral form sothat energy becomes smallest between the liquid-crystal moleculespositioned at 90 to 290°.

These liquid-crystal molecules arrayed in the spiral form are rearrangedin parallel with or perpendicular to a direction of an electric fielddue to the dielectric anisotropy of the liquid-crystal molecules byapplying voltage across the liquid crystal layer, thereby to loose thespiral structure thereof. The transmitted light amount is changed insuch a manner that, when the liquid-crystal molecules are perpendicularto the surface of the substrate, it exhibits a light state, whereas whenthe liquid-crystal molecules are in parallel therewith, it exhibits adark state. Also, the state of such liquid-crystal molecules iscontinuously changed in accordance with the applied voltage, and thetransmitted light amount is changed in accordance with the change of thestate of the molecules. Therefore, a gradation between the bright(transmitted) state and the dark (non-transmitted) state, that is, ahalftone is obtained by properly controlling applied voltage.

Obtaining the halftone is very effective in coloring, and the device cancope with full-coloring if a response speed of the liquid crystal issatisfactory.

The nematic liquid crystal has a low response speed of 100 msec, andtherefore does not provide a sufficient characteristic for display of ananimation or the like which requests a high-speed response.

Also, because the nematic liquid crystal has the fluidity, if the deviceis used in a standing state, the liquid crystal is gathered in a lowerportion of the device, whereby the lower portion of a cell has such ashape as to be swelled. As a result, since the thickness of the cell islargely changed within the device, coloring or a color shade isproduced, or the response of the liquid crystal is not uniform eventhough the same voltage is applied thereto.

Recently, because it is desired that the screen of the device is madelarge and the response speed thereof is made high, the above-mentionedproblems of the nematic liquid crystal comes more serious.

On the other hand, the LCD using the ferroelectric liquid crystal hasalso been developed. The ferroelectric liquid crystal can performswitching operation at high speed of several tens μsec because theliquid-crystal molecules have spontaneous polarization. Theferroelectric liquid crystal or the antiferroelectric liquid crystal hasspontaneous polarization, thereby to enable high-speed operation at sucha response speed of several to several hundreds μsec. Thus, it respondsat high speed more than about three digits.

In the liquid-crystal electro-optical device using the ferroelectricliquid crystal or the antiferroelectric liquid crystal, theliquid-crystal molecules can be oriented in accordance with a regulatingforce of orientation if at least one of substrates is subjected to anorientating process. These liquid-crystal molecules have a laminarstructure in which they are regularly piled on each other from onesurface of the substrate toward the other surface thereof. Also, theyhave a laminar structure in a direction parallel to the substrate.

Because of such layer structures, the ferroelectric liquid crystal orantiferroelectric liquid crystal is poor in fluidity, and in the casewhere the device is in a standing state, there is advantageous in thatthe thickness of the cell is kept constant, thereby to enable uniformdisplay without liquid crystal being gathered in the lower portion ofthe device like in the case of a nematic liquid crystal.

Naturally, in an SmC* phase exhibited by the ferroelectric liquidcrystal material, liquid crystals are oriented so that the long axis ofthe liquid-crystal molecules is inclined by a certain inclined anglewith respect to a normal (almost parallel to the substrate) of a layerprovided in the liquid-crystal material, and this forms a spiralstructure in which the liquid-crystal molecules have the direction oforientation vector which is twisted from one layer toward another layerin a bulk state, and because the spontaneous polarization having theliquid-crystal molecules is offset as a whole, ferroelectricity cannotappear.

Therefore, there has been proposed a liquid-crystal electro-opticaldevice of the so-called surface stabilizing type exhibitingferroelectricity by Clerk. In the fundamental structure, theferroelectric smectic liquid-crystal material is held between a pair ofsubstrates having the electrodes, and the liquid-crystal molecules arearranged in parallel with the substrate and optically uniaxiallyoriented so that a layer having a liquid-crystal material is formedperpendicular to the substrate or inclined with respect to thesubstrate. At this time, an interval between the pair of substrates isset to about 1 μm so that the spiral structure taken by theliquid-crystal material in the bulk state is loosened. Further, as aresult of loosing the spiral structure, the directions of the orientingvectors taken by the liquid-crystal molecules are in two stableorienting states, that is, bistable orienting states.

With the above-mentioned structure, the polarity of an electric fieldapplied to a pixel electrode is inverted so that a high-speed responsecan be made between the above-mentioned two states by torque resultingfrom a product of spontaneous polarization possessed by the liquidcrystal and the electric field applied by the electrodes.

The orientation of the spontaneous polarization possessed by theliquid-crystal molecules per se is changed by 180° (hereinafter referredto as “inversion”) by applying voltage between the substrates. Theliquid-crystal molecules has an orientation which is changed by acertain angle with respect to the optically uniaxially orientingdirection, and the orientation of the liquid-crystal molecules isinverted by applying voltage, thereby to perform switching operationfrom a bright (transmission) state to a dark (non-transmission) state,or from the dark state to the bright state.

Since the liquid-crystal electro-optical device using nematic,ferroelectric or antiferroelectric liquid crystal utilize the opticalanisotropy of the liquid molecules, it has polarizing plates outside ofboth the substrates to obtain an electro-optical characteristic.

In the case of using the ferroelectric or antiferroelectricliquid-crystal material, an optical axis of one polarizing plate ismatched with a direction in which one orienting state is exhibited ineither of two stable states, and the other polarizing plate is disposedso as to be optically axially perpendicular to the one polarizing plate.

As a method of uniaxially orienting the liquid-crystal molecules, therehas been known a method of forming a means for providing an orientingregulating force, which makes the liquid-crystal material uniaxiallyoriented (hereinafter referred to as “uniaxial orientation means”), on asurface which is in contact with the liquid-crystal material of thesubstrates, between which the liquid crystal is held. The rubbing methodhas been typically known. The rubbing method is a method in which anorientation film having a thickness of 100 to 500 Å, which is usuallymade of organic macro-molecules or the like, is formed on a surfacehaving the electrode of the substrate, and the surface of theorientation film is rubbed with cloth or the like in one direction(rubbing process), thereby to provide an optically uniaxial orientingregulating force which allows the liquid-crystal molecules to bearranged on the orientation film in one direction. The surface of thesubstrate or the electrode may be directly subjected to the rubbingprocess. The rubbing method is widely used in the TN-type or STN-typeliquid crystal electro-optical device using the nematic liquid crystal,and also most generally used in the ferroelectric liquid crystal as anexcellent orienting method which is simple and easy in making the areaof the liquid crystal large.

Since the ferroelectric liquid crystal has a high orderliness and alayer structure, once the liquid crystal is oriented, the orientationthereof is not disordered as far as the layer structure is notdestroyed. Therefore, it is not limited to the orientation using therubbing method, and even in the orienting method using no orientationfilm, that is, performing only an initial orientation, such as ashearing method, a magnetic orienting method, a temperature gradationmethod or the like, the liquid-crystal molecules are sufficientlyoriented, thereby to enable switching operation. However, these methodsare used experimentally, however, because they require much time fororienting the liquid-crystal material and are improper for manufacturingof a large-area device so as to be not practical, they are not much usedindustrially.

Also, as another method, there is a rhombic vapor deposition method inwhich SiO or the like is obliquely vapor-deposited with respect to thesurface of the substrate, however, there is a problem in productivity.Further, when the rhombic vapor deposition method is applied to thelarge-area substrate, there arises such a problem that differences invapor-deposition angle, vapor-deposition orientation or the like betweenthe respective points on the substrate cannot be ignored. Therefore, inthe current ferroelectric liquid-crystal electro-optical device, therubbing method is used as the orienting method which is widelyindustrially used.

Further, because the ferroelectric liquid crystal or the ferroelectricliquid crystal can be switched at a higher speed by about three digitsin comparison with the nematic liquid crystal, an on-state and anoff-state are controlled every display frame to perform gradationdisplay in accordance with a display time, that is, to enable so-calledframe gradation display. A digital gradation display withmulti-gradations can be performed by controlling the on/off period inthe form of a digital value by using TFTs. The details are disclosed inJapanese Patent Unexamined Publication No. 6-102486 published Apr. 15,1994 by Konuma et al.

In this case, an amorphous silicon TFT may be used for the TFT. However,for the purpose of allowing the TFT to cope with the high-speedswitching operation of the ferroelectric liquid crystal and of obtaininga higher speed, a multi-gradation and a high contrast ratio in thedigital gradation display, injection of charges into a pixel isnecessary to perform more smoothly. For this reason, there is used acrystalline silicon TFT which is operated at higher speed than theamorphous silicone TFT by about four digits and capable of allowinglarge current necessary for sufficiently inverting spontaneouspolarization to flow.

When an optically uniaxially orientation means is provided on a surfaceof substrates between which ferroelectric or antiferroelectricliquid-crystal material is interposed between the substrates with theorientation means being in direct contact with the liquid crystal, therehas arisen a problem on the switching operation of the liquid-crystalmolecules.

For example, in the case of using a rubbing method, in a process wherethe liquid-crystal material is gradually cooled after it has beeninjected into the cell, although the rubbing direction and the orientingvector have been arranged in parallel with each other in the SmA phase,the liquid-crystal molecules provide an inclined tilt angle with respectto a normal of the smectic layers when the SmA phase is transit to theSmC* phase. Therefore, the orienting vector of the liquid-crystalmolecules is not arranged in parallel with the rubbing direction, as aresult of which a bistable stable can be obtained. However, since theabove-mentioned rubbing direction exists in an intermediate positionbetween the two stable states of the liquid-crystal molecules, theliquid-crystal molecules are affected by the optically uniaxialorientation controlling force during the switching operation, thereby toobstruct the switching operation of the liquid-crystal molecules.

On the other hand, although the orienting method using a physical meanssuch as the above-mentioned shearing method, the magnetic orientingmethod, the temperature gradation method is not so practical for massproduction, because what produces the optically uniaxial orientationregulating force does not exist after the liquid-crystal material isoriented, the switching operation is not obstructed so that an excellentswitching characteristic is obtained.

Therefore, in the ferroelectric liquid-crystal electro-optical devicewhere an optically uniaxially orientation means is formed on a surfacewhich is brought in contact with the liquid-crystal material to orientthe liquid-crystal molecules, there have arisen such problems that theswitching speed is lowered, the switching operation is insufficientlyperformed or the like, in comparison with the liquid-crystalelectro-optical device where the liquid-crystal molecules are orientedby the shearing method, the magnetic orienting method, the temperaturegradation method or the like.

Further, in the liquid-crystal electro-optical device using theferroelectric liquid crystal or the antiferroelectric liquid crystal,more particularly, in the so-called surface stabilizing ferroelectricliquid crystal (SSFLC) having a substrate gap of several μm and astructure for restraining the spiral structure of the liquid-crystalmolecules, because it has the bistable property, the obtained lighttransmission state has only two bright and dark states, as a result ofwhich the halftone obtained by using the nematic liquid crystal couldnot been obtained. That is, the amount of the transmitted light couldnot be continuously changed in accordance with the state change of theliquid-crystal molecules.

In the case where the polarity of an electric field is inverted toswitch between a first state and a second state, the SSFLC deviceperforms the switching operation between the above-mentioned two statesif the liquid crystal is driven by the strength of the electric fieldmore than a saturation voltage. However, when the strength of theelectric field is gradually changed, switching is not performed byuniformly changing the amount of the transmitted light of the entireliquid-crystal material in a region to which the electric field isapplied, but the following switching is usually performed. For example,when switching is made from the first state to the second state, aregion where the first state is inverted into the second orienting state(hereinafter referred to as “domain”) occurs in a region where the firststate is exhibited. Under the condition, when the strength of theelectric field is further increased, an area of the domain is enlargedthereby to move to the second state.

One of methods of obtaining a halftone in the liquid-crystalelectro-optical device using the ferroelectric liquid crystal or theantiferroelectric liquid crystal, using the above-mentioned property, isthe area gradation method.

Observing a process of inverting the liquid-crystal molecules of theferroelectric liquid crystal or the antiferroelectric liquid crystalwith a polarization microscope, voltage is applied so that thedark-state region occurs in the bright-state region or the bright-stateregion (hereinafter referred to as “domain”) occurs in the dark-stateregion in a specified region to which voltage is applied. Further, whenvoltage is kept applied, the area of each domain is widened in such amanner that the bright state comes to the dark state or the dark statecomes to the bright state as the whole specified region.

The area gradation method is to control the area of the bright or darkdomain within one pixel by controlling applied voltage, using the factthat the dimensions of the domain are slightly changed with the changeof the applied voltage, thereby to obtain a halftone.

Further, in the surface stabilizing type liquid-crystal electro-opticaldevice using the ferroelectric liquid crystal or the antiferroelectricliquid crystal, there is a pixel dividing method as another method ofobtaining a halftone. This method is to constitute one pixel by aplurality of small pixels so as to obtain a halftone by combination oftwo bright and dark states of the respective small pixels.

For example, when one pixel is constituted by four small pixels, thedarkest or brightest state makes all of the four small pixels in thedark or bright state. Also, when a halftone is to be obtained, forexample, one of four small pixels is kept in the dark state whereasthree remaining pixels are kept in the bright state, whereby a halftonehaving the transmitted light amount of 75% is obtained as one pixel incomparison with the brightest state.

Thus, when a halftone is to be obtained in the liquid-crystalelectro-optical device using the ferroelectric liquid-crystal or theantiferroelectric liquid crystal, it must rely on the above-mentionedarea gradation method which controls the dimensions of the domain, thepixel dividing method which falsely represents one pixel by a pluralityof small pixels, or the like.

However, in the area gradation method, because the inversion of theferroelectric or antiferroelectric liquid crystal is rapid, inparticular, the domain is largely expanded even though an appliedvoltage value is slightly changed, the width of voltage capable ofrealizing the area gradation is remarkably narrowed and it has ahysteresis. For this reason, it is difficult to control the domain areaby the applied voltage of several mV unit. Also, when the appliedvoltage is lowered, a response speed is remarkably low, as a result ofwhich uniform display is not enabled. Furthermore, it is difficult toelevate the resolution of display, and therefore this method has notbeen practical.

Further, in the pixel dividing method, the efficiency is low because aplurality of pixels are used for one pixel, and also there istechnically a limit to increase the number of pixels by reducing thearea of one pixel. Also, it is improper to make the resolution high.

Still further, in the conventional surface stabilizing type liquidcrystal electro-optical device using a ferroelectric liquid crystal oran antiferroelectric liquid crystal, a low-voltage drive could not beexpected because it has a high threshold value.

Further, in the conventional surface stabilizing type liquid crystalelectro-optical device, the orienting process subjected to a pair ofsubstrates is different between both the substrates so that theorienting stability of the liquid-crystal material is kept monostable,and the strength of the electric field is changed, as a result of whichgradation display is performed. However, even in this method,consequently the inversion with the domain is made at the switchingoperation, and the same difficulty as the above-mentioned bistable typefollows. Therefore, it is not sufficient as the gradation display.

Therefore, in the liquid-crystal electro-optical device using theferroelectric or antiferroelectric liquid-crystal material, it has beendesired to provide a structure which can perform an excellent halftonegradation display.

Further, when the frame gradation method is used in the active matrixtype antiferroelectric liquid-crystal electro-optical device, in orderto perform high-speed and high-contrast display, it is required that theinversion of the liquid-crystal molecules of the ferroelectric liquidcrystal at the time of applying a signal is conducted in an extremeshort time, the inversion is sufficient, and the state of theliquid-crystal molecules after conversion is kept constant without anychanges. The state of the liquid-crystal molecules is mainly determinedin accordance with the strength of voltage applied to the electrodes ofboth the substrates.

By the way, there has been well known that an impurity having chargestransferred from the liquid crystal or the orientation film exists inthe device, and there occur surplus charges which allow voltage to begenerated in a direction reverse to applied voltage when applyingvoltage. These charges freely move within the liquid-crystal materialwhich is held between both the substrates with application of voltage. Alot of these charges move to reach the surface of the orientation film,and because the orientation film is naturally insulative, the chargesthen move no more in such a manner that they are accommodated on aliquid-crystal interface of the orientation film between the orientationfilm and the liquid-crystal layer (a layer of the liquid-crystalmaterial).

These charges cause a problem which is of disadvantage to theliquid-crystal electro-optical device. For example, action which cancelsvoltage applied between the electrodes is produced, resulting indecrease of contrast. For example, when pulsed voltage is applied bydriving the TFT, there occurs such a two-steps response that thetransmission or non-transmission switching is not rapid in such a mannerthat, after the transmission or the non-transmission is switched once,it is further switched with a small delay, or attenuation is generatedimmediately after switching operation. In order to solve this problem,it is required that applied voltage is made larger than voltagenecessary for inverting the spontaneous polarization. However, this isnot a satisfactory countermeasure.

When voltage is applied between the electrodes, the state of theliquid-crystal molecules is not stabilized because the charge amountwithin the liquid-crystal layer is changed as a time elapsed. Further,the liquid-crystal molecules which have been electrically attracted bythe charges stored in an interface between the orientation film and theliquid-crystal has larger voltage required for change of the state thanthe liquid-crystal molecules within the liquid-crystal layer, which arenot attracted. Therefore, the liquid-crystal molecules within theliquid-crystal layer are not changed in state together, but, the lighttransmission characteristic which is most important as thecharacteristics of the liquid-crystal electro-optical device is notstabilized.

Then, as the liquid-crystal electro-optical device, the display isunstable, the display speed is unavoidably lowered without making use ofthe high speed capability of the liquid crystal material, and thecontrast is lowered. In particular, when performing frame gradationdisplay, the number of gradations is limited.

In order to solve this problem, there is an attempt in which theorientation film material relaxing the storage of charges is selected,or a method in which SiO or the like is obliquely vapor-deposited on theelectrodes instead of using the orientation film of an insulating film.However, in such methods, it takes time to conduct a large number ofpreliminary experiments, which causes the costs to rise, and also itseffect is changed in accordance with combination of the materials used.Therefore, such methods are not general. Also, there is a method ofremoving an impurity by purifying the liquid-crystal. However, in thismethod, the purified liquid crystal which is usable is very slight sothat it is very improper to mass-productivity. Further, there is amethod in which charges existing within the liquid-crystal layer isabsorbed or coupled by using charge transfer complex or the like in sucha manner that positive or negative charges are canceled or neutralized.However, it is difficult to measure and insert the charge transfercomplexes by the amount necessary for completely canceling chargeswithin the device, as a result of which surplus charge transfercomplexes move within the liquid-crystal layer, likewise as theabove-mentioned charges.

As mentioned above, there have been proposed various methods forcanceling a factor which causes change of voltage applied to theliquid-crystal layer, that is, charges existing within theliquid-crystal layer, which is a factor for changing the liquid-crystalmolecules as a time elapsed to un-stabilize the optical characteristicsof the device, however, it is difficult to readily and completely cancelsuch a factor.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide aliquid-crystal electro-optical device and a method of manufacturing thesame, which are capable of eliminating the inhibition of the switchingof liquid-crystal molecules, which results from the fact that adirection of an optically uniaxial orientation regulating force anddirections of two stabilizing states exhibited by the liquid-crystalmolecules are different from each other in the SmC* phase, which is aproblem in a method of forming an optically uniaxially orientation meanson the surfaces of substrates between which a ferroelectricliquid-crystal material is held, in particular, when the rubbing methodis used for the ferroelectric liquid crystal, so that the uniaxialorientation regulating force does not obstruct switching operation ofthe liquid-crystal molecules.

Another object of the invention is to provide a structure in which theregulating force for uniaxially orienting the liquid-crystal material isexerted only when the liquid-crystal material is initially orientedduring a process where a liquid crystal is injected between thesubstrates and thereafter the liquid-crystal material is graduallycooled, and after the liquid-crystal material is uniaxially oriented,what generates the uniaxial orientation regulating force does notexists.

That is, the object of the invention is to realize a ferroelectricliquid-crystal electro-optical device excellent in switchingcharacteristics and industrially superior in productivity bysubstantially reducing or eliminating the orientation regulating forceof the uniaxially orientation means.

Still another object of the invention is to provide a liquid-crystalelectro-optical device using ferroelectric or antiferroelectricliquid-crystal material in which a spiral structure exhibited by theliquid-crystal material in a bulk state is restrained, to performoptical switching without occurrence of a domain, and a method ofmanufacturing the same.

Yet still another object of the invention is to provide a liquid-crystalelectro-optical device capable of readily realizing a change incontinuous gradation and a halftone in accordance with a change inapplied voltage, by using ferroelectric liquid crystal orantiferroelectric liquid crystal which can make an area of the devicelarge and a processing speed of the device high, as in nematic liquidcrystal, and also a method of manufacturing the same.

Yet still another object of the invention is to provide a liquid-crystalelectro-optical device of an active matrix type using ferroelectricliquid crystal having a crystalline silicon TFT with high performance,which is capable of performing high-speed multi-gradation display andhas high contrast ratio, in which an adverse effect caused by undesiredcharges within a liquid-crystal layer is removed to realize an increasein a processing speed of the device and stabilization of an opticalcharacteristic.

In order to solve the above-mentioned various problems, a first aspectof the present invention has been achieved by provision of aliquid-crystal electro-optical device in which a ferroelectric orantiferroelectric liquid-crystal material is held between a pair ofsubstrates, an orientation controlling force (an uniaxial orientationmeans), which allows said ferroelectric or antiferroelectricliquid-crystal material to be optically uniaxially oriented, is exertedon at least one of inner surfaces of said pair of substrates, and meansfor restraining said orientation controlling force is provided on thesurface on which said orientation controlling force is exerted. That is,the invention is characterized in that there is provided a means for atleast partially isolating the optically uniaxial orientation means fromthe liquid-crystal material.

In the present invention, in order to obtain the above-mentionedstructure, resin is provided between the uniaxial orientation means andthe liquid crystal layer. That is, said uniaxial orientation meansallows said liquid-crystal material to be oriented at least its initialorienting stage, and said resin functions as a means for reducing anadverse effect of the uniaxially orientation means on the liquid crystalat the switching operation of the device.

Also, in the present invention, said resin may be in the form of a filmor in the form of a large number of grains (or convex-shape). Therefore,there are a case where the entire surface of the liquid-crystal layer iscovered with the resin, and a case where only a part of theliquid-crystal layer is discontinuously covered with the resin.

Further, it is not always necessary that said resin is interposed onlybetween the uniaxially orientation means and the liquid-crystalmaterial, that is, said resin may exist on an interface between theliquid-crystal material and a surface brought in contact with theliquid-crystal material. The surface brought in contact with theliquid-crystal material may be, for example, an electrode surface, aninsulator such as a silicon oxide other than the uniaxially orientationmeans.

Also, the resin used in the present invention is made of insulatingmaterial.

Further, the uniaxially orientation means includes an orientation filmwhich has been subjected to a rubbing process.

Further, the above-mentioned liquid-crystal electro-optical device inaccordance with the present invention is characterized in that one of apair of substrates is provided with a switching element connected to apixel electrode to perform active matrix type drive.

Still further, another aspect of the present invention has been achievedby provision of a method of manufacturing the above-mentionedliquid-crystal electro-optical device. That is, there is provided amethod of manufacturing a liquid-crystal electro-optical devicecomprising the steps of: holding a mixture into which a ferroelectric orantiferroelectric liquid-crystal material is mixed with uncured resinbetween a pair of electrodes having electrodes on both of inner surfacesthereof and an optically uniaxially orientation means on one or both ofthe inner surfaces thereof; uniaxially orienting said liquid-crystalmaterial in accordance with an orientation controlling force of saidorientation means; and subsequently curing said uncured resin to providecured resin between the liquid-crystal material and a surface brought incontact with the liquid-crystal material.

Further, in the method of manufacturing the above-mentionedliquid-crystal electro-optical device, the invention is characterized inthat the uncured resin comprises ultraviolet curable resin.

Further, still another aspect of the present invention has been achievedby provision of a method of manufacturing a liquid-crystalelectro-optical device in which a mixture into which a ferroelectric orantiferroelectric liquid-crystal material is held between a pair ofsubstrates having electrodes on both of inner surfaces thereof and anoptically uniaxially orientation means on one or both of the innersurfaces thereof; means for restraining an orientation controlling forceof said optically uniaxially orientation means is provided on saidoptically uniaxially orientation means; and said liquid-crystal materialis oriented in accordance with the orientation controlling force of saidoptically uniaxially orientation means, the method comprising the stepsof: allowing the temperature of said liquid-crystal material to risefrom the room temperature to the temperature at which saidliquid-crystal material exhibits the SmA phase or the N* phase; andafter that the temperature is maintained for a given time, cooling saidliquid-crystal material to the temperature of the SmC* phase.

The present invention will be described with reference to FIG. 1. Shownin FIG. 1 is a conceptual diagram showing a simple matrix typeliquid-crystal electro-optical device in accordance with theabove-mentioned invention. In FIG. 1, reference numerals 1 and 2 denotetransparent substrates; 3 and 4, pixel electrodes; 5, an orientationfilm which is subjected to a rubbing process and constitutes anoptically uniaxially orientation means for arranging liquid crystal orthe like in a given direction after injecting the liquid crystal; and 7,ferroelectric liquid-crystal material. The liquid-crystal material 7 isuniaxially oriented in accordance with the orientation film 5. Resinfilms 6 which constitute means for restraining an orientationcontrolling force of the orientation film is formed between theorientation films 5 and the liquid-crystal material 7. Polarizing plates9 and 10 are provided on the outer surfaces of the transparentsubstrates 1 and 2.

In manufacturing the liquid-crystal electro-optical device, after theliquid-crystal material held between a pair of transparent substrates 1and 2 each having the electrode 3 or 4 and the orientation film 5 as theuniaxially orientation means with a substrate interval determined by aspacer 8 is oriented in accordance with the orientation film 5, a resinfilm which restrains the orientation controlling force may be formed onthe orientation film.

In more detail, a mixture into which liquid-crystal material is mixedwith uncured resin to which a reaction initiating agent is added isheated until it comes to the isotropic phase and injected between a pairof transparent substrates having the electrodes and the orientationfilms, and thereafter gradually cooled, as a result of which theliquid-crystal material is uniaxially oriented by the orientation films.Thereafter, the uncured resin is coated on the oriented means and curedby means for curing the uncured resin mixed into the liquid-crystalmaterial.

At this time, because the resin is cured after the liquid-crystalmaterial is arranged in accordance with the orientation means, the resincan be cured on the orientation film in the form of a film while apreferable orienting state before curing is maintained. The resin whichhas been cured does not adversely influence the orientation of theliquid-crystal material.

With the above-mentioned aspect of the invention, switching operationcan be performed at high speed, orientation defects can be prevented,and undesired charges can be removed.

In the above-mentioned aspect of the invention, the orientation film isobtained by forming a film made of organic polymeric resin such aspolyimide or the like on the substrates and the electrodes and thensubjecting the film to a rubbing process, likewise as the conventionalorientation film. The rubbing process may also be the same as theconventional one.

As other cases, if the orientation film is an orientation means foruniaxially orienting the liquid-crystal material by the surfacecharacteristic of a surface brought in contact with the liquid-crystalmaterial, the invention is applicable thereto. A case where thesubstrate or the electrode surface is directly subjected to rubbing orthe like so as to provide an uniaxially orienting force can be appliedin the same way. The rhombic vapor deposition film can be alsopracticed.

Also, as the resin film 6 for restraining the orientation controllingforce, there can be used a polymeric resin or the like.

It is desirable that material of the resin film 6 as means forrestraining the orientation restraining force in the present inventionexhibits a mixed state of the resin film material with theliquid-crystal material at a high-temperature, and is separated from theliquid-crystal material in a state where the temperature is lowered.Also, because of curing resin in a state where the resin is held betweentwo substrates, it is remarkably desirable to contain no solvent inuncured resin. Further, because the separation of liquid-crystalmaterial from resin and formation of liquid-crystal material in anoriented state greatly depend on the temperature, it is desirable tocure resin by a factor different from the temperature. Taking suchmatters into consideration, it is preferable to use an ultravioletcurable resin as an uncured resin and ultraviolet radiation as curingmeans.

Further, the density of resin material in a mixture of resin materialand liquid-crystal material is arbitrary, however, it is proper to setthe density to 20% or less.

In the liquid-crystal electro-optical device shown in FIG. 1 inaccordance with the invention, the liquid-crystal material 7 is not incontact with the orientation film 5 due to the resin film 6 formed onthe surface of the orientation film so as to be isolated therefrom.Therefore, the orientation controlling force of the orientation film onthe liquid-crystal material is restrained.

Alternatively, even though the liquid-crystal material 7 and theorientation film 5 are partially in contact with each other because theresin film 6 is thin, the orientation controlling force is substantiallyrestrained by existence of the resin film 6. Thus, in the presentinvention, while the liquid-crystal material is oriented by theorientation film constituting the uniaxially orientation means, theorientation controlling force of the orientation film after then issubstantially lowered or becomes null. Therefore, the orientationcontrolling force of the orientation film can be prevented fromobstructing the switching operation of liquid-crystal molecules.

Further, by making the density of resin material added in liquid-crystalmaterial high or by controlling the kind of the orientation film or thecuring method or the like in order to form the resin film 6, there is acase where the resin (21) is formed in a column-shape between twosubstrates. However, because the column-shaped resin is formed after theliquid-crystal material is oriented, there is almost no influence of theliquid-crystal material on orientation. The column-shaped resin canprevent the destroy of the layer structure in such a manner that asubstrate interval is prevented from expanding so as to be kept constantin the case where an area of the display unit is enlarged or the like.

Further, in the above-mentioned liquid-crystal electro-optical device inaccordance with the invention, occurrence of orientation defects isreduced in comparison with the conventional liquid-crystalelectro-optical device without a resin film. As a result, the contrastratio as the device can be improved.

Still further, when the resin material used for the resin film 6 has ahigh insulating property, because it becomes to be an insulating film,it has a function of a short-circuit preventing film for preventing theshort-circuit between the upper and lower electrodes.

Also, in the liquid-crystal electro-optical device using the usualferroelectric liquid crystal, when the failure of orientation occurs,such failure is repaired by a method in which, after the liquid-crystalmaterial is heated to the temperature at which it comes to the Iso(isotropic) phase, it is cooled to the liquid-crystal phase. However, inthe present invention, because the device which has been completed onceis reduced in orientation controlling force of the uniaxiallyorientation means due to the resin film, the oriented state is notsufficiently repaired even if this method is used.

However, in the device of the invention, it is ascertained that theliquid-crystal material is not in the Iso phase, but is heated until itbecomes in the SmA* phase or the N* phase, and then its temperature iskept for a given time, as a result of which the orientation state isrepaired. Therefore, in the device of the invention, even though thefailure of the oriented state occurs, it can be repaired.

That is, the above-mentioned liquid-crystal electro-optical device isheated to the temperature indicated below in accordance with the kind ofthe liquid-crystal material, then held at that temperature for a giventime, and thereafter gradually cooled.

First, as the temperature,

(1) In the case of liquid-crystal material having Iso-N*-SmA-SmC*-Cryphase system, the temperature exhibiting the N* phase or the SmA phaseis set.

(2) In the case of liquid-crystal material having Iso-SmA-SmC*-Cry phasesystem, the temperature exhibiting the SmA phase is set.

Subsequently, it is desirable to hold the above-mentioned device to theabove temperature for several minutes or more, preferably for 10 to 60minutes.

With the above-mentioned method, after a mixture of liquid-crystalmaterial and resin material is injected and gradually cooled, theorienting property of the device in a state where resin is cured inaccordance with the invention can be improved, and even in the devicewhere the failure of orientation has occurred, a preferable orientingproperty can be obtained, thereby to improve the contrast ratio.

Further, when the resin film 6 is formed in accordance with theinvention, the undesired charges caused by impurities or the likecontained in the liquid-crystal material substantially disappear by thecleavage of the reaction initiating agent and curing of resin material.Accordingly, if voltage is applied between electrodes, current flowsonly when the spontaneous polarization of the liquid-crystal material isinverted, in such a manner that undesired current does not flow when itis not inverted. As a result, more stable and higher-speed switchingoperation can be realized.

The above-mentioned structure of the invention is effective in thesimple matrix type liquid-crystal electro-optical device, and alsoeffective in the active matrix type liquid-crystal electro-opticaldevice.

With the above-mentioned structure of the invention, after theliquid-crystal material is oriented, the optically uniaxial orientationcontrolling force on the liquid-crystal material is not exerted orlowered, thereby to prevent the switching operation of theliquid-crystal molecules from being obstructed. As a result, theswitching operation can be made at high speed. Also, the defect oforientation can be reduced, and occurrence of short-circuit between theelectrodes can be prevented.

Also, even in a state where the uniaxially orienting property isrestrained, the orienting property of the liquid-crystal material can beimproved and a defect of orientation can be repaired.

Further, in the above-mentioned liquid-crystal device, the presentinvention is characterized in that the switching operation of theabove-mentioned liquid material caused by an electric field applied tothe above-mentioned electrodes is performed without occurrence of adomain.

Still further, in the above-mentioned liquid-crystal device, the presentinvention is characterized in that the spiral structure of theferroelectric liquid crystal or the antiferroelectric liquid crystal isloosened when no electric field is applied, and the direction of theorienting vector of the liquid-crystal molecules is continuously changedin accordance with the magnitude of an electric field applied.

Still further, particularly an active matrix driving is appropriate forthe liquid-crystal device of the present invention. This is because, inthe case of the simple matrix type, voltage applied to liquid crystalcannot be maintained for a sufficient time because the bistability ofthe liquid-crystal molecules is weakened by the resin, as a result ofwhich display quality cannot be elevated.

Further, in the present invention, in order to restrain the formation ofa domain at the time of the switching operation of liquid crystal, theproportion of monomers contained in the uncured resin is heightened.That is, the proportion of the monomer is set not lower than 60 weight %although it depends upon a molecular weight of the monomer or otherconditions.

A case where the present invention is used in the active matrix typedisplay device will be described with reference to FIG. 2. In FIG. 2,reference numerals 11 and 12 denote transparent substrates; 13 is anopposed electrode; 14 is a pixel electrode; 15 is a thin-film transistor(TFT) as a switching element; 16 is an uniaxially orientation means forarranging liquid-crystal material such as an orientation film or thelike in a given direction; 17 is a resin film; 18 is a ferroelectricliquid-crystal material. The liquid crystal material 18 is uniaxiallyoriented in accordance with the orientation means 16. Polarizing plates19 and 20 are provided on the outer surfaces of the transparentsubstrates 11 and 12.

The uniaxially orienting processing method used in the above-mentionedstructure can use an orientation film made of an organic high polymer orthe like, which has been subjected to a rubbing process, likewise as inthe conventional method. Also, in the rubbing condition, likewise as inthe conventional condition, the orientation film is rubbed in onedirection with a roller on which cloth is wound. The orientation filmmay be formed on both of the substrates or on only one substrate. Asother uniaxially orienting method, there can be used various orientingmethods such as the magnetic field orienting method, the shearingmethod, the temperature gradation method and the rhombic vapordeposition method.

In manufacturing this liquid-crystal electro-optical device, the cellgap is determined in accordance with spacers (not shown in the figure),a mixture of liquid-crystal material and uncured resin to which areaction initiating agent is added is interposed between a pair oftransparent substrates 11 and 12 having the electrodes 13 and 14, andthen the liquid-crystal material is uniaxially oriented. Thereafter, theuncured resin is separated between the liquid crystal and the surface ofthe orientation means or the electrodes, and cured by means for curingthe uncured resin mixed into the liquid-crystal material, thereby toform the resin film 17.

At this time, because the resin is cured after the liquid-crystalmaterial is arranged in accordance with the orientation means, the resincan be cured on the orientation film in the form of a film while apreferable orienting state of the liquid crystal before curing ismaintained. The resin which has been cured does not adversely influencethe orientation of the liquid-crystal material.

The inventors has found that, after uncured resin is mixed intoliquid-crystal material and injected between the substrates, the uncuredresin is cured, as a result of which action of undesired chargesexisting in the liquid crystal layer which make the state of liquidcrystal unstable can be removed.

As this action, it is considered that the above-mentioned undesiredcharges are taken in by the resin when the resin material is cured, or areaction initiating agent generally mixed into the uncured resin isdiffused in the liquid-crystal material and cleaved when the resin iscured to produce charges, whereby the undesired charges are absorbed bythe charges thus produced or coupled therewith.

According to the invention, the movement of charges and storage ofcharges on an interface between the orientation film and theliquid-crystal are eliminated. Therefore, when voltage is appliedbetween the electrodes, spontaneous polarization can be rapidly andsufficiently inverted. Further, a change in a display state afterinversion switching as a time elapsed can be removed. Furthermore,because no liquid-crystal molecules to be absorbed on the substratesexist, a state of the whole liquid-crystal layer between the electrodesis changed uniformly when voltage is applied thereto, to thereby achievea more stable optical characteristic. Consequently, display having ahigh contrast ratio at high speed can be realized.

Naturally, the optically uniaxially oriented ferroelectric liquidcrystal exhibits a property that the liquid-crystal molecules exist atany positions on a side surface of a cone having an axis which is normalto the smectic layer at the same probability, while the liquid crystalmolecules are inclined with a given angle with respect to a normal ofthe layer in the SmC* phase, and the directions of orienting vectors ofthe liquid-crystal molecules are free. This state is called “gold stonemode”. It is considered that the above-mentioned surface stabilizingdevice performs the switching operation in which the direction of theorienting vector of the molecules is limited to specified two directionsin the gold stone mode.

It has been considered that if the switching operation which is free ofthis limitation can be realized, when an electric field is applied toliquid-crystal material so as to be continuously changed, all of theliquid-crystal material in a region where the electric field is appliedis not accompanied by occurrence of domains so that the switchingoperation in which the transmitted light amount is uniformlycontinuously changed in accordance with the strength of the electricfield.

In particular, since a method of performing gradation display inaccordance with the strength of an electric field is already conductedin the TN- and STN-type liquid-crystal electro-optical device, there isan advantage that this technique can be applied as it is.

With the structure of the invention, there is obtained the switchingoperation in which the transmitted light amount is uniformlycontinuously changed in accordance with the strength of the electricfield in such a manner that the liquid-crystal material in the wholeregion where the electric field is applied is not accompanied byoccurrence of domains. In manufacturing, the substantially sameprocesses as those of the conventional surface stabilizing device areused to perform high productivity.

It is considered that the liquid-crystal electro-optical device of theinvention stands in a state where the orienting vector of the liquidcrystal molecules can be freely taken, which is different from theconventional surface stabilized type device. As in a liquid crystalelectro-optical device in which a spiral structure of a ferroelectricliquid crystal is eliminated due to the narrow cell gap, it becomespossible to switch the liquid crystals uniformly without forming domainsand to exhibits gradational display in accordance with a magnitude of anapplied electric field. Therefore, the gradation display can beperformed by the strength of an electric field at a remarkable highspeed.

In the present invention, it is considered that the resin film has afunction of relaxing an anchoring effect of the orientation film or theelectrodes to the liquid crystal.

Further, the response of the liquid-crystal molecules is improved, andin the case of driving the liquid-crystal material, the inversion ofliquid crystal molecules between brightness and darkness is in one step,whereas, in the conventional bistable type, such an inversion state isin two steps because of the formation of domains. Thus, the rapidity ofa response is significantly improved.

Furthermore, in the above-mentioned structure of the invention, athreshold value when switching is lowered in comparison with theconventional bistable device. For this reason, a low-voltage drive canbe performed in comparison with the conventional bistable device.

In the above-mentioned device of the invention, apart from a case wherea transmitted light amount is uniformly changed over the entire pixelportions, there is a case where there occurs a state in which a domainoccurrence (inversion) mixedly exists in a minute region while thetransmitted light amount is uniformly changed, depending upon amanufacturing condition such as liquid crystal or resin material to beused or a resin curing condition. Even in such a case, the switchingoperation can be continuously performed in accordance with the magnitudeof applied voltage.

There is a case where the above-mentioned resin is formed in the form ofcolumn between two substrates when the density of resin material addedinto liquid-crystal material is heightened. This is a useful method inthe case where the substrate interval is necessarily kept constant, suchas a case where the area of a display unit is enlarged.

Furthermore, after the resin is cured, the liquid-crystal material isheated to the temperature at which the material exhibits the N* phase orthe SmA phase, and then at that temperature, it is maintained constantfor 10 minutes or more, preferably for 10 to 30 minutes. Thereafter, theliquid-crystal material is gradually cooled again. With this method, theorienting state of the liquid-crystal material can be improved.

Also, viewing a display portion of the device after the resin isseparated and deposited from a substrate surface, if the ratio of anarea occupied by the resin cured in the form of a column is 0.1 to 20%,satisfactory performance as a liquid-crystal electro-optical device canbe obtained.

Further, the function for removing the action of undesired charges wasalso obtained by cleaving a reaction initiating agent by ultravioletradiation or the like after only the reaction initiating agent which isusually added to resin on the market is mixed into liquid-crystalmaterial. Also, the amount of a reaction initiating agent to be added tothe resin may be changed, or resin may be previously divided into resinmaterial (monomers or oligomer) and a reaction initiating agent so thatthey are individually mixed with each other.

Further, according to the present invention, transmission andnon-transmission of each pixel are controlled in accordance with aplurality of frames, whereby gradation display can be performed. Thatis, in the above-mentioned electro-optical device, one frame is dividedinto N (N is the natural number having numeral of 2 or more) sub-frameshaving duration different from each other, and if the shortest durationof the sub-frame is T₀, a displaying method that the duration of thosesub-frames is any one of T₀, 2T₀, 2²T₀, 2^(N)T₀ is enabled.

In the structure of the present invention, although the liquid-crystalmaterial has no bistability, the bistability of the liquid-crystalmaterial per se is not necessary because it performs the active matrixtype drive. Also, because of this, gradation display is enabled inaccordance with the strength of an electric field. Therefore, accordingto the present invention, the gradation display at high speed and withhigh contrast can be realized with a halftone produced by a framegradation and a halftone produced by an electric field due to domainlessswitching operation together. These halftones may be used independentlyfrom each other, or both may be combined with each other to therebyobtain a liquid-crystal electro-optical device at very high speed, withmulti-gradation display and with high quality.

In the liquid-crystal device described in connection with FIGS. 1 and 2,the resin brought in contact with the liquid crystal is film-shaped,however, as described above, it is not always necessary that the resinis in a continuous-film-shape. That is, there is a case where a largenumber of minute resins which are grain-shaped or convex-shaped arebrought in contact with the liquid crystal so as to be deposited. Anexample of the liquid-crystal device having such a structure will bedescribed with reference to FIG. 3. In this case, an example of thesimple matrix type liquid-crystal electro-optical device is shown,however, the active matrix type device using TFTs or the like is alsousable, as described above.

On transparent substrates 1 and 2 having electrodes 22 and 23,orientation means 24 and 25 for optically uniaxially orientingliquid-crystal molecules are formed on at least one surface of thesesubstrates.

A substrate interval is uniformly controlled by a spacer 28. Thesubstrate interval is narrow sufficient to suppress the spiral structureof the liquid-crystal molecules. Also, these substrates 1 and 2 arefixed with a sealing agent 29. Liquid-crystal material 26 is heldbetween the substrates. The liquid-crystal material 26 is opticallyuniaxially oriented in accordance with the orientation means 24 and 25.

On the other hand, a plurality of minute grains 27 in contact with thesurface of the liquid-crystal material are mainly formed on theorientation means 24 and 25. The grains 27 are made of resin. Polarizingplates 30 and 31 are disposed on the outer surfaces of the transparentsubstrates 1 and 2.

When the orientation means are formed only on the side of any one of thesubstrates, protrusions 27 are formed, for example, on the orientationmeans 24 and the transparent substrate 1 or electrodes 23 on thesubstrate 1. Also, when an insulating film, a ferroelectric thin film orthe like is formed on one or both of the substrates so as to be incontact with the liquid-crystal material 26, the protrusions 27 areformed on those films.

As the optically uniaxially orienting method, apart from the rubbingmethod using the orientation film, various methods such as the magneticfield orienting method, the shearing method, the temperature gradationmethod, and the rhombic vapor deposition method can be used.

In manufacturing the above-mentioned liquid-crystal electro-opticaldevice, uncured resin is mixed with ferroelectric liquid crystal orantiferroelectric liquid crystal, heated until it becomes in theisotropic phase and more mixed. This mixture is then injected in betweenthe substrates and cooled until the liquid crystal re-exhibits the SmC*phase (usually the room temperature). In this process, the liquidcrystal is oriented in accordance with an orientation controlling forceof the uniaxially orientation means, and an excellent extinctionposition can be ascertained under a polarization microscope. The resinis separated and deposited in such a manner that it is expelled from themixture to between the liquid-crystal molecules or between the layers(between smectic layers). After the resin is nearly completely separatedfrom the liquid crystal, it is cured and rendered insoluble to theliquid crystal. Since these resins are expelled, separated and depositedas the liquid crystal is oriented, no orientation of the liquid crystalis disturbed.

The substrate after the resin is cured was observed by an SEM (scanningtype electronic microscope) after the liquid-crystal material isevaporated. As a result, a plurality of minute protrusions constitutedby resin having a height of about 10 nm and a diameter of 500 nm orless, typically several tens to several hundreds nm can be ascertained.The protrusions exist so as to be uniformly dispersed all over thesurface, and there is also portions where a plurality of protrusions arepartially linked together.

In this way, on a surface brought in contact with the liquid-crystalsurface, that is, on the surface of the substrate, the transparentsubstrate, the orientation film, the insulating film and the like, aplurality of minute resins can be disposed in the form of a grain.

Then, the switching operation, which makes the transmitted light amountcontinuously change without occurrence of domains by controlling appliedvoltage, is enabled, thereby being capable of obtaining a halftone.Further, within a region to which the same voltage is applied, forexample, in one pixel, the nearly same gradation can be obtained. As aresult of observing the switching state by a polarization microscope,the existence of domains is not ascertained at least visually.

Also, in order to constitute resin into minute grains, it is preferableto use resin which has low viscosity and liable to be along theorientation of liquid crystal, and it is preferable to contain a largeamount of low molecule resin (hereinafter referred to as “monomer”)although it depends on the molecule weight.

Usually, resin consists of monomers, oligomer (high polymeric resin) anda reaction initiating agent. This resin is mixed into the liquid crystalmaterial at about 1 to 20%, preferably about 1 to 10%.

It is desirable that the component of resin material is organized sothat the amount of monomers contains 2% by weight or more with respectto a mixture of liquid-crystal material and resin material, and mixedinto the liquid-crystal material.

Further, it is desirable that the component of resin material isorganized so that the amount of monomers is 40% by weight or more ofresin material, preferably, 60 to 90% by weight, and mixed into theliquid-crystal material.

As the amount of monomers is reduced, the number of resin grains formedis decreased so that switching of continuously changing the transmittedlight amount without occurrence of a domain and switching of bright anddark states with occurrence of a domain is likely to mixedly exist, oronly the latter switching is likely to occur. On the other hand, as themonomer amount is increased, switching of continuously changing thetransmitted light amount without occurrence of a domain is conducted,however, optical characteristics such as the contrast ratio tend to belowered.

Further, the monomer is preferably composed of acrylic.

By thus composing the resin, in the liquid-crystal electro-opticaldevice prepared, on the surfaces of the substrate, the electrode on thesubstrate, the orientation film or the like, resin can be formed intograins having a height of several tens nm and a diameter of about 500 nmor less, typically several tens to several hundreds nm.

Furthermore, after the resin is cured, the liquid-crystal material isheated to the temperature at which the material exhibits the N* layer orthe SmA layer, and at this temperature, the material is maintainedconstant for ten minutes or more, preferably for ten to thirty minutes.Thereafter, the liquid-crystal material is cooled to the roomtemperature, as a result of which the orienting state of theliquid-crystal material may be improved.

Also, in the liquid-crystal electro-optical device of the invention, itis extremely effective to provide the structure of the active matrixtype driving having switching elements such as thin-film transistors,thin-film diode or the like on the respective pixels.

With the above-mentioned structure, in the liquid-crystalelectro-optical device using ferroelectric liquid crystal orantiferroelectric liquid crystal, the transmitted light amount iscontinuously changed to thereby obtain a halftone. As its reason, apartfrom the fact that the above-mentioned anchoring force of theorientation film is lowered, the following reasons are considered.

Observing the state of switching operation in the conventionalliquid-crystal electro-optical device using a ferroelectric liquidcrystal or antiferroelectric liquid crystal through a polarizationmicroscope, it is ascertained that a large number of domains of a darkstate appear in a bright state or a large number of domains of a brightstate appear in a dark state by gradually increasing a magnitude of anapplied voltage, and the respective areas are gradually enlarged(hereinafter, referred to as “grow”). That is, the switching operationof the ferroelectric liquid crystal or the antiferroelectric liquidcrystal comes to chain-reactive switching operation in which, with apart of liquid-crystal molecules being inverted as a start, otherliquid-crystal molecules existing around the part of liquid-crystalmolecules are inverted one after another.

On the other hand, if the resin is formed into a plurality of minutegrains on the substrate as in the present invention, they exist betweenthe layers or the adjacent liquid-crystal molecules in such a way thatthey have a size and a configuration of the degree that the orientationof the liquid-crystal molecules is not disturbed. Thus, it is consideredthat the chain of the inversion is interrupted by the resin in the formof protrusion, as a result of which further inversion of the peripheralliquid-crystal molecules is not induced.

That is, it is considered that these protrusions on the substratesprevent the adjacent liquid-crystal molecules from being inverted in thechain reactive manner, as a result of which the liquid-crystal moleculesor the extreme minute domains do not induce the inversion of theliquid-crystal molecules around the inverted ones, but the respectiveliquid-crystal molecules are independently inverted.

Therefore, it is expected that, within a specified region, for example,within one-pixel region, extremely minute regions exhibiting a brightstate or a dark state appear at a specified rate by a specified appliedvoltage, and the transmitted light amount is continuously changed byapplied voltage without occurrence of the domain to thereby obtain ahalftone.

Observing the switching operation of the liquid-crystal electro-opticaldevice in accordance with the present invention under the polarizationmicroscope, it was ascertained that applied voltage value is changedwhereby the transmitted light amount is uniformly and continuouslychanged so that the entire region to which voltage is applied is changedfrom a bright state to a dark state, or from the dark state to thebright state without occurrence of a domain.

In the above-mentioned liquid-crystal electro-optical device of thepresent invention, within such a voltage applied region, for example,within one pixel, the transmitted light amount is continuously anduniformly changed with applied voltage value. Therefore, compared withthe conventional area gradation method and the pixel dividing method, anarea necessary for obtaining the gradation can be remarkably reduced tothereby provide a liquid-crystal electro-optical device with highresolution and multi-gradation.

Further, the above-mentioned liquid-crystal electro-optical device ofthe present invention is characterized by its switching characteristic.

FIG. 4 shows an optical characteristic in the case where theconventional surface stabilizing liquid-crystal electro-optical deviceis driven by a square wave of ±1.5 V.

In FIG. 4, the optical characteristic to the applied voltage whenswitching from a dark state to a bright state or from the bright stateto the dark state exhibits two-steps response characteristic. That is,in a switching start point, the optical characteristic is rapidlychanged, and thereafter slowly changed to thereby complete the switchingoperation.

On the other hand, FIG. 5 shows an optical characteristic in the casewhere the liquid-crystal electro-optical device of the present inventionis driven by a square wave of ±1.5 V.

In FIG. 5, the optical characteristic is rapidly changed from a start ofswitching to a completion thereof throughout the whole region.

Considering the above difference, it is expected that, in the two-stepresponse in the conventional liquid-crystal electro-optical device shownin FIG. 4, an initial rapid change in the optical characteristicexhibits a state in which the liquid-crystal molecules or the minutedomains are switched on several portions, whereas a slow change in theoptical characteristic in the second step exhibits a state in which theliquid-crystal molecules or the minute domains are switched, accordingto which their peripheral liquid-crystal molecules are switched in thechain manner so that the domains are enlarged.

On the other hand, in the rapid response in the liquid-crystalelectro-optical device of the present invention shown in FIG. 5, it isconsidered that, because the liquid-crystal molecules and the minutedomains are switched in the entire region, the optical characteristic israpidly changed from the start of switching to a completion thereof.

Further, as is apparent from this, compared with the conventionaldevice, in the liquid-crystal electro-optical device of the presentinvention, because a high-speed and sufficient switching operation isconducted even at low voltage, drive voltage can be lowered.

Thus, in the liquid-crystal electro-optical device using theferroelectric liquid-crystal or antiferroelectric liquid-crystal inaccordance with the present invention, a continuous gradation change anda halftone due to a change of applied voltage can be readily obtained.Therefore, transmitted light or reflected light is switched at highspeed, and the liquid-crystal electro-optical device havingmulti-gradation and high resolution can be realized. In addition,large-sized device can also be easily obtained. Further, drive voltagecan be lowered.

In the present invention, whether the switching operation is followed byoccurrence of a domain or uniformly continuously changed depends on theamount of monomers contained in the uncured resin material mixed intothe liquid-crystal material.

The uncured resin material consists of low molecular monomers (molecularweight of 1000 or less), high molecular monomers (molecular weight of1000 or more) and a reaction initiating agent. When the amount ofmonomers are small, switching accompanied by the occurrence of a domainis made, however, as the amount of monomers is increased, a region whereeach domain is expanded is reduced while the number of regions where adomain occurs is increased. That is, under this state, there is providedbistability (memory property).

Further, if the amount of monomers is increased, it comes to uniform andcontinuous switching without occurrence of domains. In this state, thebistability (memory property) is not exhibited.

In particular, if the amount of monomers in the resin material has 40%by weight or more, preferably 60% or more, more preferably 80% or more,uniform and continuous switching without occurrence of domains can beattained.

Also, when the amount of oligomer contained in the resin material isincreased, resin cured in the form of a column is increased. Conversely,when the amount of oligomer therein is decreased and the amount ofmonomers is increased, resin cured in the form of a column is decreased.

The above and other objects and features of the present invention willbe more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a liquid crystal device inaccordance with a first embodiment of the present invention;

FIG. 2 shows a cross-sectional view of a liquid crystal device inaccordance with a second embodiment of the invention;

FIG. 3 shows a cross-sectional view of a liquid crystal in accordancewith another example of the present invention;

FIG. 4 shows an optical characteristics in the case where theconventional SSFLC device is driven by a square wave;

FIG. 5 shows an optical characteristics of the liquid crystal device ofthe present invention;

FIGS. 6A and 6B show a waveform obtained by applying a voltage across aliquid crystal device of the present invention;

FIGS. 7A and 7B show a waveform obtained by applying a voltage across aconventional liquid crystal device;

FIG. 8 is an inter-atomic force microphotograph showing a substratesurface after forming a resin in accordance with the present invention;

FIG. 9 is an inter-atomic force microphotograph showing a substratesurface before forming a resin of the present invention;

FIG. 10 shows an optical response of a liquid crystal device of a secondexample in this invention;

FIG. 11 shows a transmissitivity-voltage characteristics of liquidcrystal devices of the present invention and the prior art;

FIG. 12 shows a response characteristics of liquid crystal devices ofthe present invention and the prior with respect to an input voltage;

FIG. 13 shows a response speed-input voltage characteristics withrespect to liquid crystal devices of the prior art and the presentinvention;

FIG. 14 shows waveforms for driving an pixel in accordance with adriving method of the present invention;

FIGS. 15 and 16 shows one pixel of an active matrix circuit of thepresent invention; and

FIGS. 17A and 17B are SEM photographs showing the surface of thesubstrates on which a resin is formed in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described with reference tothe accompanying drawings.

First Embodiment

In this embodiment, a simple matrix type liquid-crystal electro-opticaldevice shown in FIG. 1 is prepared and the respective characteristicevaluation was conducted. The substrates 1 and 2 of a liquid-crystalcell are formed of soda-lime glass having an area of 300×400 mm and athickness of 1.1 mm. The pixel electrodes 3 and 4 made of ITO (indiumtin oxide) are formed on the substrates 1 and 2 by a sputtering method,and are then subjected to patterning through a photo-resist, to therebyprepare the simple matrix type liquid-crystal electro-optical device.

The orientation film material is made of polyimide resin, for example,LQ-5200 (made by Hitachi Kasei), LP-64 (made by Toray), RN-305 (made byHitachi Chemical) or the like, and in this embodiment, LP-64 was used.The orientation films were formed by coating the material diluted with asolvent such as N-methyl-2-pyrolidone or the like on both thesubstrates. The coated substrates were heated at 250 to 300° C., in thisembodiment, at 280° C. for 2.5 hours so that the solvent was dried andthe coated films were converted into an imide and cured. The thicknessof the films after being cured was 300 Å.

Subsequently, the orientation film is rubbed. The rubbing operation ismade in the usual manner, and in this embodiment, the orientation filmwas rubbed by a roller having a diameter of 130 mm on which cloth madeof rayon, cotton or the like was wound at the rotational speed of 450rpm in one direction. A roll pushing height was 0.1 mm and a stage speedwas 20 mm/sec. In this manner, the orientation films 5 were formed.

Next, as the spacer 8 for maintaining the cell interval constant, silicaparticles called “shinshikyu” produced by Shokubai Kasei corporationhaving a diameter of 1.5 μm were spread on one substrate. On the othersubstrate, for the purpose of fixing two substrates, a two-liquid epoxyadhesive is printed and coated on the periphery of the substrate as asealing agent through the screen printing method, and thereafter the twosubstrates fixedly adhered to each other.

The mixture of the liquid-crystal material 7 and the uncured polymericresin is injected into the cell. As the liquid-crystal material, theferroelectric liquid crystal of phenylpyrimidine was used. The liquidcrystal has a phase series of Iso-SmA-SmC*-Cry. A phase transitiontemperature of Iso-SmA was 85° C., and that of SmA-SmC* was 79° C. Otherthan the above, various kinds of ferroelectric liquid-crystal materialsuch as biphenyl or phenyl naphthalene can be used. As the polymericresin, an ultraviolet curable resin on the market was used. Theliquid-crystal material and the uncured polymeric resin are mixed witheach other at the ratio of 95:5% by weight. The mixture is stirred atthe temperature at which it comes to the isotropic phase so as to beuniformly mixed with each other. The phase transition temperature of themixture was lowered more than that of only the liquid-crystal materialby 5 to 20° C.

The mixture was injected under vacuum while the liquid-crystal cell andmixture were kept at 100° C. After injection, the liquid-crystal cellwas gradually cooled at the rate of 2 to 20° C./hr, in this embodiment,3° C./hr.

The orientation state of the liquid-crystal cell was observed under thecrossed-nicol with a polarization microscope. As a result, there wasobtained an extinction angle at a certain rotational angle, that is, astate in which light incident to one polarizing plate is not transmittedthrough the other polarizing plate as if the light is interrupted. Thismeans that the liquid-crystal material is uniformly oriented.

Also, at this time, when the stage was turned by about 20° from theextinction angle, there was no light leakage caused by birefringence ina field of view of a microscope, but black-state portions were dotted asthey were. Since uncured resin does not exhibits the birefringencity,the black-state portions result from allowing the uncured resin to beseparated from the liquid-crystal material and deposited into the formof a column.

Subsequently, for the purpose of curing the polymeric resin in themixture injected into the cell, ultraviolet radiation was appliedthereto. The ultraviolet radiation was applied in a direction normal tothe surfaces of the substrates from both sides of the cell with thesubstantially same intensity. By doing so, in comparison with the casewhere ultraviolet radiation is applied from only one direction, thethicknesses of the resin films formed on both the substrates can be madeidentical to each other. This is because there is a case where theorientation controlling force for the orientation film cannot besufficiently restrained. An irradiation intensity is 3 to 30 mW/cm², inthis embodiment, 10 mW/cm², and an irradiation time is 0.5 to 5 minutes,in this embodiment, 1 minute.

After the ultraviolet radiation, the orientation state of theliquid-crystal cell was observed under the polarization microscope inthe above-mentioned manner. As a result, almost no change was seen inthe orientation state. No influence of ultraviolet radiation on theorientation state was found.

Next, the optical characteristics of the liquid-crystal cell wasmeasured. The measuring method is that, in a polarization microscopehaving a light source of a halogen lamp, a triangular wave of ±30 V and5 Hz is applied to the liquid-crystal cell under the crossed-nicol, andthe intensity of transmitted light of the cell is then detected by aphoto-multiplier. The contrast ratio measured at that time is 100, whichhas satisfactory characteristics as a liquid-crystal electro-opticaldevice. Here, the contrast ratio means a ratio of the intensity oftransmitted light when voltage of 30 V is applied and the intensity oftransmitted light when voltage of −30 V is applied. On the other hand,in the liquid-crystal electro-optical device constituted by a singlesubstance of the liquid-crystal material without mixing of resin, thecontrast ratio was 80 under the identical conditions.

Subsequently, in the liquid-crystal electro-optical device in accordancewith this embodiment, a current-to-voltage characteristic was measured.FIG. 6A shows a waveform obtained by applying a triangular waveform of±30 V and 5 Hz to a pair of electrodes in the liquid-crystal cellconstituted in accordance with the present invention, to measure appliedvoltage and inter-electrode current by an oscilloscope. The value ofcurrent is obtained by measuring voltage between both terminals of aresistor having 100 kΩ connected in series to one electrode. As shown inFIG. 6B which schematically shows the waveform of FIG. 6A, current 32flowing when spontaneous polarization of the ferroelectricliquid-crystal material is inverted with a change in polarization of anelectric field is rapidly changed, that is, a response speed isremarkably high. Other than the current component 32 and the capacitancecomponent 33 between the pixel electrodes, there was no currentcomponent.

FIG. 7A shows a result obtained by measuring a current-to-voltagecharacteristic by an oscilloscope likewise in the conventionalstructural liquid-crystal cell (the same conditions except that no resinis used). As shown in FIG. 7B which schematically shows the waveform ofFIG. 7A, the current component 34 when the spontaneous polarization isinverted is enlarged in width in comparison with the liquid-crystal cellof the invention shown in FIG. 6B, from which it is understood that theresponse speed is low. It is considered that this is because theorientation controlling force of the orientation film interferes theinversion of the spontaneous polarization. A current component 35appears after a slight delay from switching of the spontaneouspolarization. Since such surplus current flows, the response speed andthe contrast ratio were lowered. It is considered that this is caused byexistence of surplus charges due to impurities or the like in theliquid-crystal material.

When the whole cell is viewed by eyes, the existence of resin cannot befound at all.

For the purpose of viewing a state of the resin film on the orientationfilm in more detail, the substrates prepared in the above-mentionedmethod was observed by an inter-atomic force microscope (AFM) after itwas cleaned by alcohol. The result is shown in FIG. 8. For comparison,the observed image of the orientation film after being rubbed but beforethe mixture of the resin material and the injection of theliquid-crystal material is shown in FIG. 9. From this figure, it isapparent that a resin film having a thickness of 10 to 30 nm is formedsubstantially all over the surface of the orientation film, and flawscaused by the rubbing process are also coated with the resin. Therefore,it is considered that the orientation controlling force of theorientation film is remarkably restrained. Also, because this resin filmis transparent and extremely thin, transmitted light is not almostattenuated.

The phase transition temperature after the resin was cured was loweredby the degree of several ° C. in comparison with a case of only theliquid-crystal material. Here, the cell was heated to 80° C. at whichthe liquid-crystal material exhibits the SmA phase, and then held atthat temperature for 10 to 60 minutes, in this example, for 20 minutes.Thereafter, the cell was gradually cooled to the SmC* at the rate of 3°C./hour. As a result, an orientation defect was remedied, and when theoptical characteristic was measure, the contrast ratio of 120 wasobtained.

On the other hand, the cell after the resin was once cured was heated to86° C. at which the liquid-crystal material exhibits the isotropicphase, and then gradually cooled in the above-mentioned manner, as aresult of which the orientation of the liquid-crystal material waspartially disordered. It is apparent from this that the resin filmexisting between the liquid crystal and the orientation film suppressesthe uniaxial orientation control force of the orientation film.

Short-circuit between the electrodes did not occur, and it wasascertained that the resin film on the orientation film functions as ashort-circuit preventing film. The short-circuiting can be more surelyprevented by increasing the amount of the resin material mixed andmaking the resin film formed thicker.

The polarizing plates 9 and 10 were provided on the outer surfaces ofthe substrates 1 and 2.

In this embodiment, as the resin material, there was used an ultravioletcurable resin commercially available on the market as it was. However,the amount of oligomer relative to the entire resin material isincreased to change the compatibility between the liquid-crystalmaterial and the resin, or the kinds of the orientation film material orthe rubbing conditions are changed thereby being capable of controllingthe amount of adhesion of the resin film to the orientation film.

Further, the kind of the orientation film or the density of rubbing ismade different between both the substrates, or ultraviolet radiation isirradiated from only one side so that the amount of adhesion of theresin can be intentionally made different between both the substrates.

Second Embodiment

In this embodiment, there is shown an example embodying the activematrix type liquid-crystal electro-optical device using crystallinesilicon TFTs (thin-film transistors) as switching elements for therespective pixels.

Formed on a silicon oxide film on a Corning 7059 glass plate (300×300mm, thickness of 1.1 mm) as a substrate are pixel electrodes comprisingITO; an n-channel type crystalline silicon TFT having the mobility of100 (cm²/Vs) which is formed by crystallizing an amorphous silicon filmby heating anneal at 600° C. for 48 hours in a hydrogen reducingatmosphere; signal electrodes and scanning electrodes formed of amulti-layer film made of chromium and aluminum; and a matrix of 640×480pixels.

Then, after an ITO is formed on another glass substrate as a counterelectrode, an orientation film is formed on only this substrate. As theorientation film material, LP-64 (made by Toray) was used. Themanufacturing method, the manufacturing conditions, the film thicknessand the rubbing conditions are the same as described in the firstembodiment.

Next, as a spacer, silica particles having a diameter of 1.5 μm weredispersed on a substrate at a side where the orientation film wasformed. On the other substrate, for the purpose of fixing twosubstrates, a two-liquid epoxy adhesive is printed and coated on theperiphery of the substrate as a sealing agent through the screenprinting method, and thereafter the two substrates fixedly adhered toeach other.

A mixture of the liquid-crystal material and uncured resin was injectedinto the cell. The liquid crystal has a phase series ofIso-N*-SmA-SmC*-Cry. A phase transition temperature of Iso-N* was 81°C., that of N*-SmA* was 69° C., and that of SmA-SmC* was 54° C. The usedresin and the used mixing ratio of the resin and the liquid-crystalmaterial are identical with those in the first embodiment. The mixturewas stirred at a temperature at which it came to the isotropic phase soas to be uniformly mixed with each other. The phase transitiontemperature of the mixture was lowered by 5 to 20° C. more than that ofthe case injecting only the liquid-crystal material.

The mixture was injected under vacuum with the liquid-crystal cell andmixture kept at 100° C. After injection, the liquid-crystal cell wasgradually cooled at the rate of 2 to 20° C./hr, in this embodiment, 3°C./hr.

The orientation state of the liquid-crystal cell was observed under thecrossed-nicol with a polarization microscope. As a result, there wasobtained an extinction position at a certain rotational angle, that is,a state in which light incident to one polarizing plate is nottransmitted through the other polarizing plate as if the light isinterrupted, and the liquid-crystal material was uniformly oriented.

Also, at this time, when the stage was turned by about 20° from theextinction state, there was no light leakage caused by birefringence ina field of view of a microscope, but black-state portions were dotted asthey were. Since uncured resin does not exhibits the birefringency, theblack-state portions are caused by allowing the uncured resin to beseparated from the liquid-crystal material and deposited into the formof a column.

Subsequently, for the purpose of curing the polymeric resin mixed intothe liquid-crystal material injected into the cell, ultravioletradiation was applied from the opposed substrate side. An irradiationintensity is 3 to 30 mW/cm², in this embodiment, 10 mW/cm², and anirradiation time is 0.5 to 5 min, in this embodiment, 1 min.

After the ultraviolet radiation, the orientation state of theliquid-crystal cell was observed under the polarization microscope inthe above-mentioned manner. As a result, the orientation state was notalmost changed. An influence of ultraviolet radiation on the orientationstate was not found.

After the substrates were cleaned by alcohol, the surfaces of both thesubstrates were observed with the inter-atomic force microscope (AFM).As a result, a resin film having a thickness of 10 to 30 nm was formedon the surfaces of both the substrates.

Then, the optical characteristic of the liquid-crystal cell wasmeasured. The inter-electrode voltage and the optical response are shownin FIG. 10. The waveform of drive voltage V_(LC) is voltage of 14 V, apulse width of 1 μs and a frame width of 16 ms. The optical response isgood as indicated by light transmittance T_(LC) shown in the figure, andthe contrast ratio at this time was 100 at the time of completion of aframe. On the other hand, the liquid-crystal cell constituted by asingle substance of the liquid-crystal material without mixing of resinhas the contrast ratio of 80 under the measurement in the identicalconditions.

The phase transition temperature after the resin was cured was loweredby the degree of several ° C. in comparison with a case of only theliquid-crystal material. Here, the cell was heated to 70° C. at whichthe liquid-crystal material exhibits the N* phase, and then held at thattemperature for 10 to 60 minutes, in this example, for 20 minutes.Thereafter, the cell was gradually cooled to the room temperature at therate of 3° C./hour. As a result, the defect of orientation was moreimproved, and when the optical characteristic was measured, the contrastratio of 120 was obtained.

Likewise, the cell constituted in accordance with the present inventionbefore the orientation is improved was heated to 55° C. at which theliquid-crystal material exhibits the SmA phase, and then held at thattemperature for 20 minutes. Thereafter, the cell was gradually cooled tothe room temperature at the rate of 3° C./hour. As a result, the defectof orientation was improved to the substantially same degree as that inthe above-mentioned case where the cell was held at the temperature atwhich the liquid-crystal material exhibits the N* phase, so that thecontrast ratio was improved.

On the other hand, the cell after the resin was once cured was heated to83° C. at which the liquid-crystal material exhibits the isotropicphase, and then gradually cooled in the above-mentioned manner, as aresult of which the orientation of the liquid-crystal material waspartially disordered. It is apparent from this that a resin film isformed on the orientation film after the resin is cured so that theuniaxially orienting property is not given to the liquid-crystalmaterial.

Polarizing plates were provided on the outer surfaces of the substratesto complete the device.

Third Embodiment

For experiment, a cell of one pixel was prepared and the evaluation ofthe respective characteristics were conducted. The fundamental structureis identical with that in FIG. 1. The size of a pixel electrode was setto 5 mm.

The orientation film material is made of polyimide resin, and in thisembodiment, LP-64 (made by Toray) was used. The orientation films werediluted with solvent such as N-methyl-2-pyrolidone or the like and thencoated on the substrates by the spin coating method. The coatedsubstrates were heated at 250 to 300° C., in this embodiment, at 280° C.for 2.5 hours so that the solvent was dried and the coated films wereimidated and cured. The thickness of the films after being cured was 300Å.

Subsequently, for the purpose of optically uniaxially orienting theliquid-crystal material and arranging the layer of the liquid-crystalmaterial normal to or inclined with respect to the substrates, theuniaxial orientation controlling force was given to the orientation filmby the rubbing method. The rubbing operation was made likewise as in theusual way, that is, the orientation film was rubbed by a roller having adiameter of 130 mm on which cloth made of rayon, cotton or the like waswound at the rotational speed of 450 to 900 rpm, in this embodiment, 450rpm in one direction. A roll pushing height was 0.1 mm and a stage speedwas 20 mm/sec.

As the liquid-crystal material, the ferroelectric liquid crystal ofphenylpyrimidine was used. The liquid crystal taken a phase series ofIso-SmA-SmC*-Cry. As the polymeric resin, an ultraviolet curable resinon the market was used. The polymeric resin is to prevent the separationof the liquid-crystal material from the mixture when the mixture isinjected, and the polymeric resin containing monomers 90% by weight isused so that the compatibility between the liquid-crystal material andthe resin is heightened. As the density of the uncured polymeric resinin the liquid-crystal material, because a resin column is formed betweenthe upper and lower substrates thereby lowering numerical aperture if alarge amount of resin is contained in the liquid-crystal resin, it ispreferable that the amount of resin is small, and therefore the uncuredpolymeric resin was mixed with the liquid-crystal material at the ratioof 95:5% by weight. The mixture is stirred at a temperature at which itcomes to the isotropic phase so as to be uniformly mixed with eachother. The transition point of the mixture from the isotropic phase tothe SmA phase was lowered by 5° C. more than that of only theliquid-crystal material.

The mixture was injected under vacuum while the liquid-crystal cell andmixture were at 100° C. at which the mixture exhibits the Iso phase.After injection, the liquid-crystal cell was gradually cooled to theSmC* phase. If the cell is rapidly cooled to the SmC* phase, a largeamount of orientation defects occur. For this reason, the liquid-crystalcell was gradually cooled at the rate of 2 to 20° C./hr, in thisembodiment, 3° C./hr as a temperature lowering rate.

The liquid-crystal cell was gradually cooled to the room temperature inthe above-mentioned method, and the orientation state of the cell wasobserved under the crossed-nicol by a polarization microscope. When thestage is turned, there was obtained an extinction position at a certainrotational angle, that is, a state in which light incident to onepolarizing plate is not transmitted through the other polarizing plateas if the light is interrupted. This exhibits that the liquid-crystalmaterial is uniformly oriented in such a manner that the orientingvectors of the liquid-crystal molecules are oriented in the samedirection within the layers and over from layer to layer.

Also, at this time, when the stage was turned by about 20° from theextinction state, there was no light leakage caused by birefringence ina field of view of a microscope, but black-state portions were dotted asthey were. This exhibits that the resin is separated and deposited inthe form of a column.

Subsequently, for the purpose of curing the polymeric resin mixed intothe above-mentioned liquid-crystal material, ultraviolet radiation wasapplied thereto. As a light source, an Hg—Xe lamp having rated power of150 W is used. The cell was positioned so that an irradiation intensityis 3 to 30 mW/cm², in this embodiment, 10 mW/cm², and ultravioletradiation was applied thereto. An irradiation time is 0.5 to 5 min, inthis embodiment, 1 min.

After ultraviolet radiation was radiated, the orientation state of theliquid-crystal cell was observed under the polarization microscope inthe above-mentioned manner. As a result, the orientation state was notalmost changed. An influence of ultraviolet radiation on the orientationstate was not found.

After the substrate was separated from the device and the liquid crystalwas cleaned and removed from the substrate by alcohol, the resinremaining on the substrate was observed by a scanning type electronicmicroscope. As a result, columnar resin which had fixed both thesubstrates could be observed. Although it depends on the kinds of resinor liquid crystal material or the curing conditions, in most of thecases, the cured resin has a side view of a trapezoid or a rectangle, atop cross-section (face viewed from a direction normal to the substrate)of a round trapezoid or rectangle, a circle or an elliptical, and isplateau-shaped as a whole. These resin has an upper cross-section whosesize (a diameter in the case of a circle) is about several μm to severaltens μm and whose height is equal to a substrate interval. There arevarious shapes of resin such that the height is about 1/10 of thethickness, or the size of the upper section is nearly equal to theheight so as to be die-shaped.

The shape of resin is also changed depending on the phase transitionseries of the liquid-crystal material, the cooling process or the like.There are a shapeless resin and a resin having a longitudinal axis inthe uniaxially orienting direction. Also, an interval between theexisting resin cured in the form of a column was about 10 to 100 μm.

Under the above-mentioned orienting state, the contrast ratio wasmeasured. The measuring method is that, in a polarization microscopehaving a light source of a halogen lamp, a triangular wave of ±30 V and5 Hz is applied between the electrodes of the liquid-crystal cell underthe crossed-nicol, and the intensity of transmitted light of the cell isthen detected by a photo-multiplier. The contrast ratio was 120.

Subsequently, the switching process of the cell was observed through thesame optical system as the above. A triangular wave having a lowfrequency was applied to the cell. Different from the switchingoperation followed by the generation of a domain as in the conventionalferroelectric liquid-crystal electro-optical device, switching betweenbrightness and darkness made the entire amount of transmitted lightuniformly change, depending on the strength of an electric field.

Then, the contrast-to-voltage characteristic was measured. The measuringmethod is that first the cell is positioned at the extinction positionwhen applying d.c. 20 V, and then voltage is increased from 0 V to 20 V,and the intensity of transmitted light is measured. The result is shownin FIG. 11. The characteristic values of the present invention areindicated by square plots, and a threshold value was about 0.8 V.

The response of the liquid-crystal material when the direction of anelectric field is inverted was measured. The states of the changes in adrive waveform and the contrast are shown in FIG. 12. At this time, thedrive waveform was a square wave of ±3 V and 5 Hz. A response waveform36 in the device according to the present invention rapidly rises afterthe polarity of the square wave is inverted, which is of a one-stepresponse.

Further, a dependency of the response of the liquid-crystal material onvoltage was investigated. The drive waveform was a square waveform of 5Hz. The result is indicated by the square plots in FIG. 13. In the cellof the present invention, a high response speed of about 1 msec isexhibited even in a low voltage region. Also, in logarithmiccoordinates, voltage and the response speed have a linear relationship.That is, the strength of an electric field and the response speed alwayshave a given relationship. This suggests that the cell of thisembodiment operates at the gold stone mode.

Subsequently, the current-to-voltage characteristic was investigated bymeasuring a current flowing between the electrodes when a triangularwaveform of ±30 V and 5 Hz is applied to the liquid-crystal cell. Therewas no current components except for a capacitance component between theelectrodes and a current flowing when spontaneous polarization of theferroelectric liquid-crystal material is inverted as the polarity of theelectric field is changed.

Next, the pulse memory property of the cell was investigated. The drivewaveform was 200 μm in pulse width and 20 ms in frame width. There issubstantially no pulse memory property.

Also, the optical switching property was investigated by applying apulse of 14V, 1 μs with a frame duration 16 ms, using a driving circuitcomposed of TFTs externally connected to the cell. As a result, anexcellent optical response is obtained, and the contrast ratio at thistime was 120 at the time of completion of a frame.

For the purpose of viewing a state of the resin film in more detail, thesubstrates prepared in the above-mentioned manner was observed by aninter-atomic force microscope (AFM) after it was cleaned by alcohol.According to this observation, a coating of polymeric resin was formedon the surface of the orientation film. Although it depends on themanufacturing conditions, the thickness of the coating was about 10 to30 nm, and the coating had minute irregularity. There were a portionwhere a resin film does not almost exist, and a portion where a resinfilm having a thickness of about 50 nm exists.

For comparison, a cell having the same structure except that no resin iscontained was observed. First, in the observation of the switchingprocess using the triangular waveform, switching accompanied byoccurrence of a domain was made. Also, as to a dependency of theintensity of transmitted light on voltage, a threshold value was about 2V as indicated by circular plots in FIG. 11. Also, the response when thepolarity of an electric field is inverted had an initial rapid rising asindicated by 37 in FIG. 12, but had a slow change from the middlethereof, which was of a two-step response. As a result of investigatinga dependency of the response speed on voltage, the response speedrapidly becomes slow when voltage is 3V or less, as indicated bycircular plots in FIG. 13, so that a relationship between the strengthof the electric field and the response speed is not linear.

Further, as a result of measuring a current-to-voltage characteristic,there was observed a peak representing an undesired current componentcaused by electric charges contained in the liquid crystal. Also, it wasfound that the current component related to the inversion of thespontaneous polarization has a low peak value and a wide width incomparison with the device constituted in accordance with the presentinvention, as a result of which it is understood that the response speedis lowered. On the other hand, the pulse memory property was relativelygood.

Fourth Embodiment

An example of the active matrix drive type device providing acrystalline silicon TFT as a switching element for each pixel will bedescribed with reference to FIG. 2.

Formed on a silicon oxide film (not shown in the figure) on a Corning7059 glass plate (300×300 mm, thickness of 1.1 mm) as a substrate 12 arepixel electrodes 14 formed of ITO; and n-channel type crystallinesilicon TFT 15 having the mobility of 100 (cm²/Vs) which is formed bycrystallizing an amorphous silicon film by heating at 600° C. for 48hours under a hydrogen reducing atmosphere; signal electrodes andscanning electrodes formed of a multi-layer film made of chromium andaluminum; and a matrix of 640×480 pixels.

Next, a film of ITO having 1200 Å was formed on a soda-lime glasssubstrate as an opposed substrate 11 by a sputtering method to providean opposed electrode. As the electrode material, SnO₂ (tin oxide) or thelike can be also used. Further, as the substrate material, inorganicmaterial such as glass or quartz, or organic material such as acrylicresin or polyethylene resin can be used.

An orientation film 16 is formed only on the substrate on which theopposed electrode is formed to provide the so-called one-sidedorientation. The orientation film material can be made of polyimide orpolyamide resin, or resin such as polyvinyl alcohol. Polyimide resin isfor example, LQ-5200 (made by Hitachi Kasei), LP-64 (made by Toray),RN-305 (made by Nissan Chemical) or the like, and in this embodiment,LP-64 was used. The formation of the orientation film was carried outentirely in the same manner as in the first embodiment.

For the purpose of optically uniaxially orienting the liquid-crystalmaterial and arranging the layer of the liquid-crystal material normalto or inclined with respect to the substrates, the uniaxial orientationcontrolling force was given to the orientation film by the rubbingmethod. The rubbing operation was made likewise as in the usual way,that is, the orientation film was rubbed by a roller having a diameterof 130 mm on which cloth made of rayon, cotton or the like was wound atthe rotational speed of 450 to 900 rpm, in this embodiment, 450 rpm inone direction. A roll pushing height was 0.1 mm and a stage speed was 20mm/sec.

It is proper that a substrate interval is 1 to 10 μm, and a spacermaterial is silica, alumina or the like. In this embodiment, in order tomaintain the cell gap constant, as a spacer, silica particles“shinshikyu” (made by Shokubai Kasei) having a diameter of 1.5 μm werespread on the substrate at a side where the orientation film is coated.On another substrate, for the purpose of fixing the two substrates, atwo-liquid epoxy adhesive is printed and coated on the periphery of thesubstrate as a sealing agent through the screen printing method, andthereafter the two substrates fixedly adhered to each other.

The mixture of the liquid-crystal material 18 and the uncured polymericresin was injected into the cell. As the liquid-crystal material, theferroelectric liquid crystal of phenylpyrimidine was used. The liquidcrystal takes a phase series of Iso-SmA-SmC*-Cry. As the polymericresin, an ultraviolet curable resin on the market was used. In order toprevent the separation of the liquid-crystal material from the resinwhen the mixture is injected, and the polymeric resin containing theamount of monomers of 90% by weight was used so that a compatibilitybetween the polymeric resin and the liquid-crystal material isheightened. As to the concentration of the uncured polymeric resin inthe liquid-crystal material, since if a large amount of resin iscontained in the liquid-crystal resin a resin column is formed betweenthe upper and lower substrates thereby lowering numerical aperture, itis preferable that the amount of resin is small, and therefore theuncured polymeric resin was mixed with the liquid-crystal material atthe ratio of 95:5% by weight. The mixture is stirred at the temperatureat which it comes to the isotropic phase so as to be uniformly mixedwith each other. The transition point of the mixture from the isotropicphase to the SmA phase was lowered by 5° C. more than that of only theliquid-crystal material.

The mixture was injected under vacuum while the liquid-crystal cell andmixture were at 100° C. at which the mixture exhibits the Iso phase.After the injection, the liquid-crystal cell was gradually cooled to theSmC* phase. If the cell is rapidly cooled to the SmC* phase, a largeamount of orientation defects occur. For this reason, the liquid-crystalcell was gradually cooled at the rate of 2 to 20° C./hr, in thisembodiment, 3° C./hr as a temperature lowering rate.

The liquid-crystal cell was gradually cooled to the room temperature inthe above-mentioned method, and the orientation state of the cell wasobserved under the crossed-nicol by a polarization microscope. When thestage is turned, there was obtained an extinction position at a certainrotational angle, that is, a state in which light incident to onepolarizing plate is not transmitted through the other polarizing plateas if the light is interrupted. This exhibits that the liquid-crystalmaterial is uniformly oriented in such a manner that the orientingvectors of the liquid-crystal molecules are oriented in the samedirection within the layers and over from layer to layer.

Also, when the stage was turned by about 20° from the extinction state,there was no light leakage caused by birefringence in a field of view ofa microscope, but black-state portions were dotted as they were. Thisexhibits that the resin is separated and deposited in the form of acolumn.

Subsequently, for the purpose of curing the polymeric resin mixed intothe above-mentioned liquid-crystal material, ultraviolet radiation wasapplied thereto. As a light source, an Hg—Xe lamp having rated power of150 W was used. The cell was positioned so that an irradiation intensityis 3 to 30 mW/cm², in this embodiment, 10 mW/cm², and ultravioletradiation was applied thereto. An irradiation time is 0.5 to 5 min, inthis embodiment, 1 min.

After ultraviolet radiation was radiated, the orientation state of theliquid-crystal cell was observed under the polarization microscope inthe above-mentioned manner. As a result, the orientation state was notalmost changed. An influence of ultraviolet radiation on the orientationstate was not found. At this time, the resin in the form of a columnallows the upper and lower substrates to adhere to each other so as toprevent a distance between the substrates from being enlarged, as aresult of which, even though the liquid crystal is enlarged in area, thelayer structure of the liquid-crystal material can be prevented frombeing destroyed.

The device thus manufactured had the contrast ratio of about 120. Atriangular wave having a low frequency was applied between theelectrodes, and the switching state was observed by a polarizationmicroscope. As a result, a region to which voltage was applied wasuniformly changed in the amount of transmitted light without occurrenceof a domain.

Polarizing plates 19 and 20 were stuck on both the substrates, and adriving circuit is connected to the device to thereby complete aliquid-crystal electro-optical device. Rewrite on one screen isperformed for 1/60 second, and the magnitude of applied voltage iscontrolled so that display with 256 gradations can be realized.

The substrates prepared in the above-mentioned manner was observed by aninter-atomic force microscope (AFM) after it was cleaned by alcohol.According to this observation, a coating of polymeric resin having athickness of about 10 to 30 nm was formed on both of the surface of theorientation film and the surface of the pixel electrodes.

Viewing the electrode portion of the liquid-crystal cell by eyes, theexistence of the resin cannot be found at all. From these results, itcan be found that, if the rate of the resin material occupying an areaof a display portion is about 0.1 to 20%, then it is not inferior to theconventional device.

In this manner, the cell having the uniform inter-electrode distance canbe manufactured. Even though the completed cell is located vertically,the uniformity of display or the like could not be recognized at all.The deformation of the substrates or the like was not generated, and thelayer structure of the ferroelectric liquid crystal used in thisembodiment was not destroyed.

In this embodiment, as the switching elements connected to the pixels,the n-channel type thin-film transistor was used. However, it may be ofthe p-channel type, or constituted by a complementary type using thep-channel type thin-film transistor and the n-channel type thin-filmtransistor. Also, it may be of a structure using a non-linear elementsuch as an MIM diode or the like.

Fifth Embodiment

In the liquid-crystal electro-optical device of the fourth embodiment,display with 32 gradations was performed by digital gradation driving.FIG. 14 shows changes of gate voltage V_(G), drain voltage V_(D), pixelvoltage V_(LC) and the transmittance TLC of the pixel for one pixel ofinterest in the display method used therein. First, as shown in FIG. 14,one frame is constituted by five sub-frames. The durations of therespective sub-frames are 0.5 msec in a first sub-frame, 8 msec in asecond sub-frame, 1 msec in a third sub-frame, 4 msec in a fourthsub-frame and 2 msec in a fifth sub-frame (In FIG. 14, a distance of therespective sub-frames is the same, accordingly one frame becomes 15.5msec. That is, if the duration of the first sub-frame is the shortestduration T₀, the durations of the second sub-frame and so on are 16T₀,2T₀, 8T₀ and 4T₀, and 32 gradations can be displayed by combination ofthe durations of these five sub-frames.

Within one sub-frame, first a square pulse signal is applied to ascanning line as gate voltage V_(G) to turn on the gate electrodes ofTFTs for pixels of one line (laterally, 640). On the other hand, tosignal lines connected to the drain electrodes of the respective TFTs, apulse train representing any one of positive and negative states isapplied as drain voltage V_(D). The pulse train includes the totalscanning number in the sub-frame interval, in this embodiment, 480pieces of information, and the respective information is synchronouswith scanning of each line. Scanning is performed for all of 480 linesto determine on-state or off-state of all the pixels, to therebycomplete one sub-frame. As mentioned above, the durations of therespective sub-frames are different from each other. During the aboveoperation, each pixel is maintained in an on-state or in an off-state bykeeping the transmittance T_(LC) constant regardless of the fact thatthe pixel potential V_(LC) gradually approaches 0 due to naturaldischarge. In this embodiment, the transmittance T_(LC) during theoperation is remarkably stabilized and not changed even though a time iselapsed, or the like.

In this way, when all the sub-frames are completed, the gradationdisplay within one frame can be digitally realized. The pulse width ofthe scanning signal applied to the gate electrode of each TFT is set to2 μsec, the wave height of the pulse is −15 V, and the data signalapplied to the drain electrode is ±10 V. In this device, theirregularity and flicker and the like of display did not appear at all,and the contrast ratio of 120 was obtained at 32 gradations.

In this case, when the data signal applied to the drain electrode wasset to ±5 V, it was operated with no trouble.

Also, the gradation display due to the number of frames is not made,one-screen rewrite is performed for 1/60 min to change the strength ofan electric field. That is, when 32-gradation display was performed bycontrolling the magnitude of applied voltage, the gradation wassatisfactorily definitely displayed.

Furthermore, 16 gradations by the number of frames and 16 gradations byapplied voltage were displayed thereby being capable of performing256-gradation display.

In this embodiment, as the switching elements connected to the pixels,the n-channel type thin-film transistor was used. However, it may be ofthe p-channel type, or constituted by a complementary type using thep-channel type thin-film transistor and the n-channel type thin-filmtransistor. Also, it may be of a structure using a non-linear elementsuch as an MIM diode or the like.

In this embodiment, as shown in FIG. 15, there was used a drive systemin which one thin-film transistor 15 was used for one pixel, TFTs of oneline are turned on by applying a signal to a scanning electrode 43connected with the gate electrode of each TFT, and a transmitted ornon-transmitted signal or a gradation signal is applied by a signalelectrode 44 connected with a source or drain electrode to performdisplay.

Other than this system, the present invention is effective to, forexample, a drive system in which rewrite is performed every pixel usingtwo TFTS as shown in FIG. 16.

Sixth Embodiment

In this embodiment, a film made of indium tin oxide (ITO) is formed asan electrode on a glass substrate of 10 cm□ by a sputtering method or avapor phase deposition method so that the film has a thickness of 500 to2000 Å, in this embodiment, 1000 Å, and then electrodes are patterned inthe form of a stripe through a usual photolithographic process.Polyimide is coated on the substrate by a spin coating method andsintered at 280° C. As polyimide, RN-305 (made by Nissan Chemical) andLP-64 (made by Toray) were used. The thickness of polyimide is 100 to800 Å, in this embodiment, 150 Å. The substrates were subjected to arubbing process to perform an uniaxially orienting process. Silicaparticles were spread on one substrate. On another substrate, sealingmaterial made of epoxy resin was formed by the screen printing method.Both the substrates have an inter-electrode distance of 1.5 μm and arefaced to each other so that the stripe-shape electrodes are orthogonalto each other, thereby forming a simple matrix type cell having thenumber of pixels of 640×480.

The liquid-crystal material used in this embodiment is CS 1014 which isferroelectric liquid-crystal made by Chisso Corporation. Ps of thisliquid crystal is 5.4 nC/cm², and a phase series is I (isotropicphase)-N (nematic phase)-A (smectic A phase)-C* (smectic C* phase).

The resin material used in this embodiment is obtained by mixing acrylicmonomers on the market having the molecular weight of about 150 to 200with urethane oligomer having the molecular weight of about 1500 to 3000at the ratio of 90:10% by weight and then mixing them with a reactioninitiating agent of about 3% by weight on the market (hereinafterreferred to as “uncured resin material”).

The liquid-crystal material and the uncured resin material 5% were mixedwith each other at the ratio of 95:5% by weight. The mixed resin washeated and stirred to 90° C. at which the liquid crystal exhibits theisotropic phase so as to be more mixed into the liquid-crystal material.As a result, the resin was uniformly mixed into the liquid-crystalmaterial.

The cell and the liquid-crystal mixture were heated at 90° C., and thengradually cooled to the room temperature at 2 to 20° C./hr, in thisembodiment, at 2° C./hr after the mixture was dispersed into the cell.After gradually cooling, the orienting state at the room temperature wasobserved by a polarization microscope. Although the resin material whichwas dotted in the cell and column-shaped could be recognized, theformation of resin on the substrates could not be recognized. However,the orientation of the liquid-crystal material, likewise as theliquid-crystal material to which no resin is added, was uniaxiallyoriented along a rubbing direction of the orientation film, resulting inan excellent extinction position.

Ultraviolet radiation was applied to the cell in such a manner that anirradiation intensity is 3 to 30 mW/cm² and an irradiation time is 0.5to 5 min, in this embodiment, 20 mW/cm² and 1 min, so that the resin iscured. After irradiation of ultraviolet radiation, the liquid crystalwas also uniaxially oriented along the rubbing direction of theorientation film, thus obtaining an excellent extinction position.

As a result of observing a change in the transmitted light with a changein applied voltage of the cell, the gradation was continuously changedfrom a dark state to a bright state or vice versa, thereby enabling ahalftone display. Occurrence of a domain could not be recognizedvisually.

Both the substrates of this cell were separated from the cell and wereleft in an oven at 200° C. for 5 hours so that liquid crystal wasvolatilized. Thereafter, as a result of observing the substrates by thepolarization microscope, it was ascertained that it was not polarized,and the resin formed on the substrates was observed through SEM.

FIGS. 17A and 17B show SEM photographs representing a fine pattern thusformed on the substrates. FIG. 17B is an enlargement of FIG. 17A. Asshown in the figures, a large number of fine protrusions made of resinhaving a height of 10 nm and a diameter of 500 nm or less, typicallyabout several tens to several hundreds nm were observed. The protrusionswere wholly uniformly dispersed on the surface thereof, and also therewere partially portions where a plurality of protrusions continued.

Also, in this embodiment, the number of pixels may be set to 1920×480,and there may be provided color filters of three colors consisting ofred, blue and green so that full-color display of 640×480 can beperformed. If it is 256 gradations, colors of about 1670 ten thousandscan be displayed.

Seventh Embodiment

In this embodiment, the structure of a device, resin material, amanufacturing method, and a mixing ratio of liquid-crystal material anduncured resin material were identical with those in the sixthembodiment. The liquid-crystal material in this embodiment wasferroelectric liquid crystal of biphenyl having Ps of 20.7 nC/cm² and aphase series of I-A-C*. The orienting state of the liquid-crystalmaterial of a cell formed was observed under a polarization microscope.As a result, likewise as in a case where no resin is mixed, theliquid-crystal material was optically uniaxially oriented along therubbing direction of the orientation film, resulting in an excellentextinction position.

As a result of observing a change in the transmitted light with a changein applied voltage of the cell, the gradation was continuously changedfrom a dark state to a bright state or vice versa, thereby enabling ahalftone display. Occurrence of a domain could not be recognizedvisually.

Both the substrates of this cell were separated from the cell and wereleft in an oven at 280° C. for 5 hours so that liquid crystal wasvolatilized. Thereafter, as a result of observing the substrates by thepolarization microscope, it was ascertained that it was not polarized,and the resin on the substrates was observed through SEM. As a result, alarge number of fine protrusions made of resin having a height of about30 nm and a diameter of about 90 nm on average were observed.

Eighth Embodiment

In this embodiment, the structure of a device, resin material, amanufacturing method, and a mixing ratio of liquid-crystal material anduncured resin material were identical with those in the sixthembodiment. However, as the uncured resin material, there was used resinmaterial obtained by mixing acrylic monomers on the market having themolecular weight of about 100 to 150 with urethane oligomer having themolecular weight of about 1000 to 2000 at the ratio of 65:35% by weightand then mixing them with a reaction initiating agent of about 3% byweight on the market.

The orienting state of the liquid-crystal material of a cell formed wasobserved under a polarization microscope. As a result, likewise as in acase where no resin is mixed, the liquid-crystal material was opticallyuniaxially oriented along the rubbing direction of the orientation film,resulting in an excellent extinction position.

As a result of observing a change in the transmitted light amount with achange in applied voltage of the cell, the gradation was continuouslychanged from darkness to brightness or from brightness to darkness,thereby enabling a halftone display between brightness and darkness.Occurrence of a domain could not be recognized visually.

Both the substrates of this cell were separated from the cell and wereleft in an oven at 200° C. for 5 hours so that liquid crystal wasvolatilized. Thereafter, as a result of observing the substrates by thepolarization microscope, it was ascertained that it was not polarized,and the resin form on the substrates was observed by an SEM. As aresult, a large number of protrusions made of resin having a height ofabout 30 nm and a diameter of about 90 nm on average were observed.

Ninth Embodiment

In this embodiment, an example of the active matrix drive typeliquid-crystal electro-optical device having a crystalline silicon TFT(thin-film transistor) as a switching element for each pixel will bedescribed.

Formed on a silicon oxide film on a Corning 7059 glass plate (300×300mm, thickness of 1.1 mm) as a substrate are pixel electrodes formed ofITO; an n-channel type crystalline silicon TFT having a mobility of 100(cm²/Vs) which is formed by crystallizing an amorphous silicon film byheating at 600° C. for 48 hours under a hydrogen reducing atmosphere,and wiring formed of a multi-layer film made of chromium and aluminum ormade of aluminum whose surface has been subjected to anodic oxidation,and a matrix of 640×480 pixels.

Next, a film of ITO having a thickness of 1200 Å was formed on asoda-lime glass substrate by a sputtering method to provide a countersubstrate. As the electrode material, SnO₂ (tin oxide) or the like canbe also used. Further, as the substrate material, inorganic materialsuch as glass or quartz, or organic material such as acrylic resin orpolyethylene resin can be used.

An orientation film is formed on only the substrate on which the opposedelectrode is formed to provide the so-called one-sided orientation. Theorientation film material can be made of polyimide or polyamide resin,or resin such as polyvinyl alcohol. Polyimide resin is for example,LQ-5200 (made by Hitachi Kasei), LP-64 (made by Toray), RN-305 (made byNissan Chemical) or the like, and in this embodiment, LP-64 was used.The orientation film was obtained by mixing the material with a solventsuch as N-methyl-2-pyrolidone or the like and then coating the mixtureon the substrates by a spin coating method. The coated substrate washeated at 250 to 300° C., in this embodiment, at 280° C. for 2.5 hoursso that the solvent was dried and the coated film was imidated andcured. The thickness of the film after being cured was 300 Å.

For the purpose of optically uniaxially orienting the liquid-crystalmaterial and arranging the layer of the liquid-crystal material normalto or inclined with respect to the substrates, the uniaxial orientationcontrolling force was given to the orientation film by a rubbing method.The rubbing operation was made likewise as in the usual way, that is,the orientation film was rubbed by a roller having a diameter of 130 mmon which cloth made of rayon, cotton or the like was wound at therotational speed of 450 to 900 rpm, in this embodiment, 450 rpm in onedirection. A roll pushing height was 0.1 mm and a stage speed was 20mm/sec.

It is proper that a substrate interval is 1 to 10 μm, and a spacermaterial is silica, alumina or the like. In this embodiment, in order tomaintain the cell gap constant, as a spacer, silica particles having adiameter of 1.5 μm were spread on a substrate at a side where theorientation film is coated. On another substrate, for the purpose offixing two substrates, a two-liquid epoxy adhesive is printed and coatedon the periphery of the substrate as a sealing agent through the screenprinting method, and thereafter the two substrates fixedly adhered toeach other.

The mixture of the liquid-crystal material and the uncured resinmaterial was injected into the cell. The liquid-crystal material used inthis embodiment is CS 1014 which is ferroelectric liquid-crystal made byChisso Corporation. Ps of this liquid crystal is 5.4 nC/cm², and a phaseseries is I (isotropic phase)-N (nematic phase)-A (smectic A phase)-C*(smectic C* phase).

The resin material used in this embodiment is obtained by mixingcommercially available acrylic monomers having the molecular weight ofabout 150 to 200 with urethane olygomers having the molecular weight ofabout 1500 to 3000 at the ratio of 90:10% by weight and then mixing themwith a commercially available reaction initiating agent of about 3% byweight.

The liquid-crystal material and the uncured resin material were mixedwith each other at the ratio of 95:5% by weight. The mixed resin washeated and stirred at 90° C. at which the liquid crystal exhibits theisotropic phase so as to be more mixed into the liquid-crystal material.As a result, the resin was uniformly mixed into the liquid-crystalmaterial to provide a liquid-crystal mixture.

The cell and the liquid-crystal mixture were heated at 90° C., and thengradually cooled to the room temperature at 2 to 20° C./hr, in thisembodiment, at 2° C./hr after the mixture was injected into the cell.After gradually cooling, the orienting state at the room temperature wasobserved by a polarization microscope. Although the resin material whichwas dotted in the cell and column-shaped could be recognized, the resinform on the substrates could not be recognized. However, the orientationof the liquid-crystal material, likewise as the liquid-crystal materialto which no resin is added, was uniaxially oriented along a rubbingdirection of the orientation film, resulting in an excellent extinctionposition.

Also, when the stage was turned by about 20° from the extinction state,there was no light leakage caused by birefringence in a field of view ofa microscope, but black-state portions were dotted as they were. Thisexhibits that the resin is separated and deposited in the form of acolumn.

Ultraviolet radiation was applied to the cell in such a manner that anirradiation intensity is 3 to 30 mW/cm² and an irradiation time is 0.5to 5 min, in this embodiment, 20 mW/cm² and 1 min, so that the resin iscured. After irradiation of ultraviolet radiation, the liquid crystalwas also uniaxially oriented along the rubbing direction of theorientation film, thus obtaining an excellent extinction position. Atthis time, the resin in the form of a column allows the upper and lowersubstrates to adhere to each other so as to prevent a distance betweenthe substrates from being enlarged, as a result of which, even thoughthe liquid crystal is enlarged in area, the layer structure of theliquid-crystal material can be prevented from being destroyed.

The switching state of the cell thus manufactured was observed by apolarization microscope. As a result, in each of pixels, the amount oftransmitted light was continuously changed without occurrence of adomain. Also, the gradation was uniform within a region of each pixel.

Polarizing plates were stuck on both the substrates, and a drivingcircuit is connected to the device to thereby complete a liquid-crystalelectro-optical device. Rewrite on one screen is performed for 1/60 min,and the magnitude of applied voltage is controlled so that display with256 gradations can be realized.

As a result of observing the substrates prepared by the above-mentionedmethod through SEM, a large number of fine protrusions having a heightof several tens nm and a diameter of about several tens to severalhundreds nm on both the surface of the orientation films and the surfaceof the pixel electrodes were observed.

In this embodiment, as the switching elements connected to the pixels,the n-channel type thin-film transistor was used. However, it may be ofthe p-channel type, or constituted by a complementary type using thep-channel type thin-film transistor and the n-channel type thin-filmtransistor. Also, it may be of a structure using a non-linear elementand a thin-film diode such as an MIM diode or the like.

Also, in this embodiment, the number of pixels may be set to 1920×480,and there may be provided color filters of three colors consisting ofred, blue and green so that full-color display of 640×480 can beperformed. If it is 256 gradations, colors of about 1670 ten thousandscan be displayed.

COMPARATIVE EXAMPLE 1

This comparative example shows an example in which uncured resinmaterial was not mixed in the cell shown in the sixth embodiment.

The orienting state of the liquid-crystal material of the cell formedwas observed under a polarization microscope. As a result, theliquid-crystal material was optically uniaxially oriented along therubbing direction of the orientation film, resulting in an excellentextinction position.

As a result of observing a change in the amount of transmitted lightwith a change of applied voltage of the cell, switching with only twostates of brightness and darkness with occurrence of a domain wasconducted, and the amount of transmitted light was not continuouslychanged.

After ultraviolet radiation having an intensity of 20 mW/cm², which isthe same as that in the sixth embodiment, and 1 min was applied to thecell, a change in the amount of transmitted light was observed whileapplied voltage was changed. Similarly, switching with only two statesof brightness and darkness followed by a domain was made.

COMPARATIVE EXAMPLE 2

An example in which resin was not cured in the cell shown in the sixthembodiment will be described.

Likewise as in the sixth embodiment, a cell was manufactured, and themixture of the liquid-crystal material and the uncured resin wasinjected into the cell. As a result of observing the orienting state ofthe liquid-crystal material of the cell prepared under a polarizationmicroscope, likewise as in the case where no resin is mixed, theliquid-crystal material was uniaxially oriented along the rubbingdirection of the orientation film, resulting in an excellent extinctionposition.

As a result of observing a change in the amount of transmitted light asapplied voltage is changed under the condition where the resin is notcured by not applying ultraviolet radiation to the cell, switching withonly two states of brightness and darkness with occurrence of a domainwas conducted, and the amount of transmitted light was not continuouslychanged.

Although the surface of the substrate of the cell was observed throughSEM in the same manner as in the sixth embodiment, no protrusionsconstituted by resin was observed.

COMPARATIVE EXAMPLE 3

In this comparative example, an example in which the mixing ratio of themonomers and the olygomers in the resin material is made different fromthat in the cell shown in the sixth embodiment 6 will be described.

As the resin material used in this comparative example, uncured resinmaterial was obtained by mixing acrylic monomers having the molecularweight of about 150 to 200 with urethane olygomers having the molecularweight of about 1500 to 3000 at the ratio of 10:90% by weight and thenmixing them with a reaction initiating agent of about 3% by weight.

As a result of observing the orienting state of the liquid-crystalmaterial of the cell prepared under a polarization microscope, likewiseas in the case where no resin is mixed, the liquid-crystal material wasuniaxially oriented along the rubbing direction of the orientation film,resulting in an excellent extinction position.

Ultraviolet radiation was applied to the cell in such a manner that anirradiation intensity is 3 to 30 mW/cm² and an irradiation time is 0.5to 5 min, in this comparative example, 20 mW/cm² and 1 min, so that theresin is cured. After irradiation of ultraviolet radiation, the liquidcrystal was also uniaxially oriented along the rubbing direction of theorientation film, thus obtaining an excellent extinction position. As aresult of observing a change in the amount of transmitted light with achange of applied voltage of the cell, switching with only two states ofbrightness and darkness with occurrence of a domain was conducted, andthe amount of transmitted light was not continuously changed.

Although the surface of the substrate of the cell was observed by anSEM, likewise as in the sixth embodiment, protrusions constituted byresin as in the sixth embodiment was not almost observed, and the stateof the surface was very flat.

As described above, the liquid-crystal electro-optical device inaccordance with the present invention can perform high speed,multi-gradation, high resolution, low-voltage drive and an increase ofits area, and also such an device can be readily manufactured. Further,the present invention can provide the liquid-crystal electro-opticaldevice which is satisfactorily excellent and proper for a display unitwhich displays high-quality image such as high vision or the like.

In the above-mentioned embodiments, ferroelectric liquid crystal isused, however, antiferroelectric liquid crystal can be also usedlikewise.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

1. A liquid crystal device comprising: first and second substrates; aliquid crystal layer comprising a ferroelectric liquid crystal providedbetween said first and second substrates; a resin disposed between saidfirst and second substrates; a spacer disposed between said first andsecond substrates; an electrode provided over at least one of said firstand second substrates for applying an electric field to saidferroelectric liquid crystal; an orientation film provided over saidfirst substrate; and a film provided over said second substrate, whereinsaid resin covers said orientation film and at least a portion of saidresin is contiguous to said orientation film and to said film providedover said second substrate, wherein said resin is formed by disposing amixture of the liquid crystal and a curable resin between said first andsecond substrates and curing said curable resin.
 2. The device of claim1 wherein said liquid crystal device is an active matrix type.
 3. Theliquid crystal device according to claim 1 wherein at least a part ofsaid resin is disposed between the liquid crystal layer and theorientation film.
 4. The liquid crystal device according to claim 1wherein said curable resin is a photocurable resin.
 5. The liquidcrystal device according to claim 1 wherein said liquid crystal layerdoes not have memory characteristics.
 6. A liquid crystal devicecomprising: first and second substrates; a liquid crystal layercomprising a ferroelectric liquid crystal provided between said firstand second substrates; a resin disposed between said first and secondsubstrates; a spacer disposed between said first and second substrates;an electrode provided over at least one of said first and secondsubstrates for applying an electric field to said ferroelectric liquidcrystal; an orientation film provided over said first substrate; and afilm provided over said second substrate, wherein said resin covers saidorientation film and at least a portion of said resin is contiguous tosaid orientation film and to said film provided over said secondsubstrate, wherein said resin is formed by disposing a mixture of theliquid crystal and a curable resin between said first and secondsubstrates and curing said curable resin and an intensity of lighttransmitted through the liquid crystal layer can be continuously changedin accordance with a strength of the electric field in an operation ofthe liquid crystal device.
 7. The device of claim 6 wherein said liquidcrystal device is an active matrix type.
 8. The liquid crystal deviceaccording to claim 6 wherein at least a part of said resin is disposedbetween the liquid crystal layer and the orientation film.
 9. The liquidcrystal device according to claim 6 wherein said curable resin is aphotocurable resin.
 10. The liquid crystal device according to claim 6wherein said liquid crystal layer does not have memory characteristics.11. A liquid crystal device comprising: first and second substrates; aliquid crystal layer comprising an antiferroelectric liquid crystalprovided between said first and second substrates; a resin disposedbetween said first and second substrates; a spacer disposed between saidfirst and second substrates; an electrode provided over at least one ofsaid first and second substrates for applying an electric field to saidantiferroelectric liquid crystal; an orientation film provided over saidfirst substrate; and a film provided over said second substrate, whereinsaid resin covers said orientation film and at least a portion of saidresin is contiguous to said orientation film and to said film providedover said second substrate, wherein said resin is formed by disposing amixture of the liquid crystal and a curable resin between said first andsecond substrates and curing said curable resin.
 12. The device of claim11 wherein said liquid crystal device is an active matrix type.
 13. Theliquid crystal device according to claim 11 wherein an intensity oflight transmitted through the liquid crystal layer can be continuouslychanged in accordance with a strength of the electric field in anoperation of the liquid crystal device.
 14. The liquid crystal deviceaccording to claim 11 wherein said curable resin is a photocurableresin.
 15. The liquid crystal device according to claim 11 wherein saidliquid crystal layer does not have memory characteristics.
 16. A liquidcrystal device comprising: a pair of substrates; a liquid crystal layercomprising a ferroelectric liquid crystal provided between saidsubstrates; a column-shape resin disposed between the pair ofsubstrates; an electrode provided over at least one of said substratesfor applying an electric field to said ferroelectric liquid crystal; anorientation film provided over at least one of said substrates; and aspacer provided between said substrates, wherein said column-shape resinis formed by disposing a mixture of the liquid crystal and a curableresin between the pair of substrates and curing said curable resin. 17.The device of claim 16 wherein said resin comprises an acrylic resin.18. The device of claim 16 wherein said resin is provided on saidorientation film.
 19. A liquid crystal device comprising: a pair ofsubstrates; a liquid crystal layer comprising an antiferroelectricliquid crystal provided between said substrates; a column-shape resindisposed between the pair of substrates; an electrode provided over atleast one of said substrates for applying an electric field to saidantiferroelectric liquid crystal; an orientation film provided over atleast one of said substrates; a spacer provided between said substrates,wherein said column-shape resin is formed by disposing a mixture of theliquid crystal and a curable resin between the pair of substrates andcuring said curable resin.
 20. The device of claim 19 wherein said resincomprises an acrylic resin.
 21. The device of claim 19 wherein saidresin is provided on said orientation film.
 22. A liquid crystal devicecomprising: first and second substrates; a liquid crystal layercomprising a ferroelectric liquid crystal provided between said firstand second substrates; a resin disposed between said first and secondsubstrates; a spacer disposed between said first and second substrates;an electrode provided over at least one of said substrates for applyingan electric field to said ferroelectric liquid crystal; an orientationfilm provided over said first substrate; and a film provided over saidsecond substrate, wherein said resin covers said orientation film and atleast a portion of said resin is contiguous to said orientation film andto said film provided over said second substrate, wherein said resin isformed by disposing a mixture of the liquid crystal and a curable resinbetween said first and second substrates and curing said curable resin,and wherein a transmitted light amount of said liquid crystal layercontinuously varies in response to voltage applied to said liquidcrystal layer.
 23. The device of claim 22 wherein said resin comprisesan ultraviolet curable resin.
 24. The device of claim 22 wherein saidliquid crystal device is an active matrix type.